A nerd is someone who is extremely passionate about a certain subject matter or topic. It can be anything from Pokemon cards to books but this person will devote many hours to this topic and know many random facts that a normal person wouldn't. Contrary to popular belief a nerd is not always someone who wants to be isolated or can't interact with another human because of their social awkwardness. Nerds come in all forms with all different kinds of personalities.
Guy: She's a total nerd; I like it. Maybe she will be as passionate about being in bed with me as she is over science.
Any person who is so obsessed with their phone, tablet, or other electronic device that they are incapable of having any direct conversation with other people, especially in places such as restaurants, clubs, bars, and on public transport.
Check out that nerd. He's been pushing those keys for twenty minutes and hasn't even noticed his food arrived ten minutes ago.
A person who is highly intelligent and shows much interest in a particular field (usually computers) but gets bullied because you don't meet the social standards of society such as following cringy trends. Though, they have a shitty school year(s) they grow up to get all the hoes and makes a 6 figure income.