What everyone has said, plus you eat waaaaayyyy tooo much food, turkey or ham (unless you are a vegetarian) lots of good deserts. Afterwards the guys sit around and watch football, the girls catch up on family goings on, you know whose pregnant, whose getting married, whose getting divorced, etc...

Anyway its basically a time to spend with your family together... Traditionally it is meant to be a time of reflection and gratitude for good things in your life, sometimes we need to be reminded of how lucky many of us are in ways we often do not realize.