Burikko is a slang term and is a combination of 'furi', meaning to pretendto be something/fake something, and 'ko', meaning child.
A burikko is a female who acts one way in front of guys, especially good looking guys and/or guys she's interested in, or authority figures that she wants to impress (e.g. teachers, bosses), and an entirely different, ruder (or..closer to her real nature) way in front of other girls/women or guys she's not interested in.
You can have male burikko (burikko danshi ぶりっ子男子), but the standard burriko is female.
You know the type. They exist everywhere. No, it's not a good thing to be called. You might call such a female in English 'fake' 'two-faced b*tch', etc.
Many Japanese burikko act very cute and innocent-sexy in front of guys they're interested in. This video is pretty good at explaining this. (But being a burikko is not a martial art, just in case.)