i am 79, live in South Americas since 30 years, speak only spanish ( and french) every day. have contact with english-speaking people maybe 1 week per year altogether, don't have english TV, don;'t have any contact with young people of any language and I don't know what a nerd is !! i think it could maybe mean somebody who is only interested in studying ? then i am a nerd !
In British English we would say 'swot', to mean someone who is very studious. A few decades ago when i was at school (though things may have changed now), the act of revising was known as 'swotting' or 'swotting up on'. 'Nerd', i think, is more modern and more American, and refers to someone who tends to be very interested in things such as science, computers etc. Difficult to categorise, for me at least!