score:4
Say "party" or "celebration;" you don't need to add anything else unless they ask.
If they do, explain it simply (eg. "my cousin's wedding for 3 days"). Do not lie to an immigration officer, on a visa application, or anywhere else, or you might not be able to re-enter the US. It's not worth it, especially with the current administration.
Upvote:23
To your comment that you want to know if you should mention your reason for travel a party or an event:
There is no harm in saying it's a party at a friend's place along with the address. The officer may or may not ask the details of a party which would go on for 3 days, that really depends on him. EDIT: This goes for a beach party too
People always travel for birthdays, bridal showers, etc. So using the word party is ok as long as you know where you would be staying for the 3 days and what the party is about.
The word event usually refers to things like a conference where you have an invitation letter and qualifications to attend it; or something similar. However, if it is an event like a concert, festival etc then can say that you're going to ABC event at XYZ place.
Just be truthful and explain it as you feel easy.