What is 'lolita'?

what is it?

Think gothic clothing and you're pretty much there. Lollita is really frilly darkish sort of emo/gothic looking costumes. I suppose it's a cuter version or something...

Lolita is a style named after the book Lolita by Vladimir Nabokov. In it an older man falls in love with a very young girl, I believe she is 12 years old, they end up getting into a sexual relationship (ew). Its a very famous book because it came out in 1955 and was very controversial. Anyway, the Lolita style of clothing is dresses and bonnets and stockings but with a dark mood, so kind of like 12 year old girl with the innocence stripped away, hence the name Lolita.

A lolita is a sexually attractive/alluring young girl.

It's also a Japanese style of clothing, inspired by Victorian and Rococo fashion, that is meant to look cute and innocent... It's not necessarily dark or gothic - that's just gothic lolita. Sweet lolita is all pastel colours and designs involving sweets and carousels. xD
There are actually pretty strict rules on what is and what isn't lolita... and they aren't costumes. Most lolitas will get pretty offended at someone calling their outfits costumes or cosplay. A lot of them can be pretty elitist about it most of the time, too. People who get it wrong, dress in lolita as a cosplay or wear cheap, badly made costumes and call it lolita are referred to as 'cosplay lolita' or 'ita-loli' ('painful lolita').