An informal particle/expression that emphasizes emotion (disdain, surprise, disgust, irony, etc.). Can mean 'things like' or 'the fact that' and often adds a dismissive or astonished tone.
彼がそんなことをするなんて信じられない。
I can't believe he would do such a thing.
初心者なんて気にしなくていいよ。みんな最初はそうだ。
Don't worry about being a beginner. Everyone is like that at first.
彼女が優勝するなんて、驚きだ。
It's surprising that she won.