Did Lord Buddha teach, or do Buddhist sects teach, about Ghosts?

Yes, he did. The example, it is one big problem of bhikkhu, who live in forests, so buddha taught to manage ghost in vinaya, many time.

But the most of western people hate ghost theory, so the tipitaka translators often avoid to translate sutta about ghost into english.

Everything such as ghost, human, deva, etc., are just causes and effects (paticcasamuppada), so ghost also is causes and effects. Ghost is not a special stuff in theravada buddhism.

Hungry ghosts are addicts afflicted with craving. The world is full of visible hungry ghosts.

Remember a lot of spiritual teachings are metaphorical, i.e. they are to help people in their lives by creating an easy way to understand a concept, like a children’s story, if we always look at things as literal, or strive for something like perhaps ghosts to be real, then perhaps we are completely missing the point, maybe they are real or maybe not

Spiritual Science Research Foundation that is there to bridge the known and unknown worlds says that around 30% of the world’s population is possessed by ghosts. You will find their web page a very interesting read. It will tell you as to how do people get possessed by ghosts.

Ghosts are real, as real as there exists life after this life. When people talk about ghosts this subject is avoided because of the uncertainty related to this topic. Questions are many, with only a few answers. Are these people good or bad, why they are here, what they want... are few such that are in the mind of us all.

How can someone be born in the realm of the hungry ghosts can be explained through “paticca samuppada”. Paticca = pati + icca, can be interpreted as getting attached to something through a liking for it or something related to it”. Then Samuppada, = “sama” (same or similar) + “uppäda” (generation), i.e., an existence (bhava) of similar quality or kind.

Thus “when one gets attached, it sets up likelihood of a new birth of similar characteristics”. For example, when someone acts with greed out of habit, and act that way during the lifetime, then it could lead to a future birth as a hungry ghost.

Thus when one cultivates such greedy (abhi)sankhara, it leads to a corresponding “bhava” in the realm of hungry ghosts. Jane Roberts once wrote a series of books based on “Seth”, a being who could “possess” her body with her permission, and spoke to her husband about various things about the world; see, for example, “Seth Speaks” by Jane Roberts (1994). Seth commented on various issues and made many predictions too.

In Sri Lanka we often come to see or hear bizzaire instances of hungry ghosts possessing some one's body. Possession is when a spirit or entity breeches your active free will in some way to get inside and take control of your body. When a desire is there whether it’s good or bad, desire is desire. At the time of death if unfulfilled desires are there, the vinnana of the said dead persons travel on pretha loka only, possess those of the living in order to fulfill these unmet desires.

What Buddha had to say about Ghosts (Preta)

“Bhikkhus, those who depart from the human realm, those will be reborn as humans or devas can be compared to the few grains of sand that I pickup on my fingernail. Those who are reborn in the lower four realms are exceedingly many, compared to the sand on this great Earth”. – Nakhasikha Sutta- The Tip of the Fingernail – SN20-2

The Samyutta Nikaya (Saṃyutta Nikāya SN, "Connected Discourses" or "Kindred Sayings") is a Buddhist scripture, the third of the five nikayas, or collections, in the Sutta Pitaka, which is one of the "three baskets" that compose the Pali Tipitaka of Theravada Buddhism. Descriptions of Pretas and pretis (female ghosts) in this Samyutta Nikaya and Petavatthu show that they come in various shapes and sizes depending on their past unwholesome kamma.

Petavatthu is part of the Khuddaka Nikaya: The "Division of Short Books" (Pali khudda = "smaller," "lesser"), consisting of fifteen books (eighteen in the Burmese edition): Petavatthu — Stories of the Hungry Ghosts.

In Petavatthu it is said that Pretas are ghostly beings devoid of happiness. They live a life of misery, being subjected to incessant pain and suffering, lack of food and clothing. The vivid descriptions found in Petavatthu highlight the extreme suffering experienced by Pretas as a result of their unwholesome kamma.

The Milinda Pañha ("Questions of Milinda") is a Buddhist text which dates from approximately 100 BCE. Milinda Pañha records a dialogue between the Buddhist sage Nāgasena, and the Indo-Greek king Milinda. According to Milinda-Pañhā, there are 4 classes of Pretas:

1. Vantasikas who feed on what have been vomited by others.

2. Khuppipasinos who suffer from being continually tormented by extreme hunger and thirst for very long periods of time.

3. Nijjhamatanhikas who are consumed by thirst, being tormented by a continual burning feeling within their bodies.

4. Paradattupa-jivi who depend on what others offer for them: They remember their living relatives and see what they do. Only this class of Pretas can receive and share in the merits when offerings are made on their behalf.

Though we believe that if we live a “good, moral life”, a rebirth in the human or even higher deva worlds is guaranteed, this is a misconception. It is because we do not know what kinds of bad kamma we have accumulated in past lives. This is why Buddha has mentioned over and over in many Suttas that it is very hard to even get a human existence (bhava) let alone a deva or a brahma rebirth.

In the “Saccasamyutta” under “Passing Away from the Animal Realm” It is said that:

... “So too, bhikkhus, those beings are few who, when they pass away from the animal realm, are reborn among human beings. But those beings are more numerous who, when they pass away from the animal realm, are reborn in hell ... in the animal realm ... in the domain of ghosts...."

under “Passing Away from the Domain of Ghosts” it is said that: ... “So too, bhikkhus, those beings are few who, when they pass away from the domain of ghosts, are reborn among human beings. But those beings are more numerous who, when they pass away from the domain of ghosts, are reborn in hell ... in the animal realm ... in the domain of ghosts...."

In the Book of Causation ( Nidanavagga ) it is said that:

… produced among the ghosts, etc., having as its object the residue of that kamma or the sign of the kamma. Therefore, because that rebirth comes about through correspondence of kamma or correspondence of, it is called "a residual result of that same kamma." It is said that at the time he passed away from hell, a heap of flesh- less cows' bones became the sign (i.e., the object of the last conscious process, which then becomes the object of the rebirth-consciousness). Thus he became a ghost (in the form of) a skeleton, as if making manifest to the wise the hidden kamma.

There is this story in the scriptures, about an old woman who was very careful about not breaking the five precepts. But she was extremely greedy; she was quite stingy, did not give much to charity, and kept all her money under her pillow. Because of that greed, she was born a peta (a hungry ghost).

Yet in the Great Book (Mahavagga) - Friends and Colleagues - Buddha says: "Bhikkhus, there may be alteration in the four great elements — in the earth element, the water element, the heat element, the air element — but there cannot be alteration in the noble disciple who possesses confirmed confidence in the Buddha. Therein this is alteration: that the noble disciple who possesses confirmed confidence in the Buddha might be reborn in hell, in the animal realm, or in the domain of ghosts. This is impossible.

Paticca samuppada (PS) or “cause and effect” can describe various stages of life. The Buddha said that the PS is deep as a deep ocean and it can be applied to any situation, because everything “in this world” obeys the basic principle of cause and effect.

As per to PS, whenever we willingly grasp something, whatever results from that action has a corresponding nature. Because one got attached willingly, a similar bhava will result: i.e., pati+ichcha leading to sama+uppada. From this, a “greedy state of mind” will result when we get attach with greed.

An excessively greedy person is like to get a “peta bhava” and be born as a peta (hungry ghost); a person who is often engaged in hateful actions towards other beings is likely develop a “hateful bhava” and is likely to be born in the niraya (hell) where there is lot of hate due to extreme suffering; an animal bhava is developed with both greed and hate.

A built-up vinnana can form a habit; as the habit gets stronger, it can be carried over to the next life, possibly in two ways: a really strong habit could lead to a “patisandhi vinnana” at the dying moment and can lead to a corresponding “bhava”, and thus one could be born in the corresponding “jati”. For example, an extremely greedy person, may acquire a “peta bhava” at the dying moment and be born as a “peta” or a hungry ghost.

Yes, the Buddha did. Here is one place: Tirokudda Sutta

Another such incident (told in the Petavatthu) is when Arhat Sariputta encountered his mother five births before who was now in one of the ghost worlds.

There are many such stories in Petavatthu, which appear in canonical texts. Buddhist Cosmology mentions 31 Planes of Existence. The realm of Hungry Ghosts is one of these realms. Average people cannot see any of these realms other than the parts of the human realm and animal kingdom. This does not mean, what we see do not exit.

Also see:

• From preta to hungry ghost by Piya Tan
• Who are the hungry ghosts? by Piya Tan