What is the "Light-Life Movement"

The Catholicism tag is completely OK, as well as the link provided in Gilbert Le Blanc's comment. The Light-Life Movement (or "Oasis movement") is Catholic, though oecumenism is one of its priorities and it was influenced by Campus Crusade for Christ, a Protestant evangelist movement. The beliefs of Light-Life Movement don't differ from Catholic norm, and the stress is on topics that gained importance in Catholic Church after Second Vatican Council, such as evangelisation or understanding the liturgy. It belongs to the charismatic current in Catholic Church.

The aim of the movement is to guide (especially young but not only) Christians to "Christian maturity" through its formation. The formation consists of three degrees, typically a year long each (15-days retreat in Summer and meeting in a small group during most of the year). The first degree focuses on prayer (especially Lectio Divina, called "Tent of Meeting" in the movement) and personal relationship with Jesus, the second on liturgy and "Exodus" from slavery of sin and the third on the Church and one's place in it. There are slightly different forms of the formation for the young, for families ("the Domestic Church") and in Poland, where the movement is strongest, there are many other variants too.

The history of the Light-Life Movement starts during Second World War by conversion of a young Polish named Franciszek Blachnicki. As a guerilla fighter against the Nazis, he was caught and sentenced to death. While waiting for execution, he read books including one about conversions of famous people - this (along with the stress from waiting for death) lead him to renounce his former atheist worldview, to accept Jesus as his personal Lord and Saviour and to promise to become a priest if he survives the war. His death sentence was changed to ten years in prison (sort of a miracle) and he survived.

Since 1954, Blachnicki lead some retreats for altar boys, a well composed mixture of prayer, education (especially to help the boys understand liturgy - there is a focus on liturgy in the movement since then) and games, which became the base of later Oases, retreats lead by Blachnicki and his successors in the movement. The retreats offered the participants great spiritual gains and virtually everyone wanted to attend retreats lead by this priest - this is the main root of the movement.

At about the same time, Blachnicki started Crusade for Abstinence, an initiative to encourage people to stop drinking alcohol and to help those who try to recover from their addiction, mostly by prayer and fast (in form of abstinence from alcohol). The original Crusade for Abstinence was banned by communist government, but it was re-established as Crusade for the Liberation of Man in 1977. Abstinence is required for animators (those who guide others through the formation) of the movement in Poland (in Czech Republic, it is just strongly recommended to join the Crusade for the animators, not strictly required).

Second Vatican Council was a big boon for the Oasis movement - the Church as a whole turned in the direction in which Blachnicki already went. Blachnicki translated the Council's documents for the movement even before they were translated oficially and the movement took the true teaching of the Council (in contrast to misunderstanding and misuse of the "spirit of the Council") as one of its goals.

Even later, there were other important events influencing the movement. I don't know the exact year (I have heard about this from a lecture by current General Moderator of the movement, Adam Wodarczyk, and I forgot some details and didn't manage to find any sources for it online and in English; AFAIK it was in late 60s, but I'm not sure, it might have been later) when Blachnicki learnt of Campus Crusade for Christ and met Josh McDowell. This lead to the evangelist and oecumenical focus in the movement and even strenghened focus on Bible, Lectio Divina and spontaneous prayer. The concepts of four spiritual laws and accepting Jesus as one's personal Lord and Saviour, that became crucial to Light-Life movent formation, have Protestant origin.

These were roots of the Light-Life Movement, but it was officially founded in 1973, when it was renamed from “The Movement of the Living Church”. The old name was often criticised ("Does it mean that the rest of the Church is dead?"), so Blachnicki divided those responsible for the movement to ten groups and let each group to propose a new name. All ten groups independently choose "Light-Life", for one of the basic principles taught in the movement (to let the light of God, his revelation and our faith change our life, or the unity of truth we know and the way we live).

The movement still has the most members in Poland, but it is active in many other countries (I've heard 30, but I'm not sure). In some, it has members mostly between Polish minority (such as in Germany), and in others, Oases have local participants mostly (such as in Czech Republic, where I joined the movement).