What is nerdy anyway?

So, my husband runs a RPG website, and one of his friends was over and they were talking about the whole RPG thing, and one of them made a comment about how they were about to get mega nerdy…. which got me to thinking… what is nerdy anyway… I mean… who gets to decide this? Why are sports less nerdy than computers? I mean… let’s take my hobby for example… is it nerdy? I sit around with a group of women creating fancy photo albums with paper and glue… so is that nerdy? Is it nerdy when you post your creation to a website? Is it nerdy if you BLOG about it… what defines cool and what definies nerdy anyway?