When you see a comment, status, picture, etc. that you really like, instead of clicking the "like" button once, out of sheer excitement you click the "like" button three times. It isn't a double like, for if you clicked the "like" button twice, it would merely "unlike" the comment, status, picture, etc. When you perform a triple like, you must immediately comment and let the person know that you have triple liked something of theirs.
Tony: *replying* I know! That was the greatest vacation ever!
John: I made so many good memories there,
I gotta triple like this picture!
Tony: You like it that much, huh?
John: Yes! It's already my background!