So how do you define a nerd?

Honestly, the one who define people as nerds are the ones who think they are that way. because they feel that the person they think are not part of a societal group or any class of people is considered weird and indifferent. and that's why they classify it as a nerd. maybe glasses is not the based on being a nerd. it's the attitude of the person and the way he/she see's in their own little world.

I think nerds are people who can have an obsession about things. They have the obsession to learn. I'm a nerd.

Let me see, based on people whom I called nerd before (not proud of it), I see it as a person who takes pride in their work, nerdy status, and occasionally suffers from social awkwardness.

One who would spend most of the time on books yea and normally would wear a thick black glasses yea.