A no life person is someone who usually has very little contact with other people, and so will rather spend their time doing things that only negatively effect their lives.
People with no life usually enjoy playing MMORPGs, Video Games.
People with no life usually enjoy the computer, video games.
And dislike, social contact, physical excersize.
Unlike nerds and geeks, no lifes actually PREFER to waste their time on unuseful things, unlike nerds who are socially akward but want to have friends.
Friends 1: Hey look at Kyle, the kid has no life, hes been inside the house for about 3 weeks now.
Friend 2: Fuck him, lets go play basketball.