Larceny is the legal term for stealing. Grand larceny is when you take something worth a lot of money, petty larceny when the stolen item is worth relatively little.
Larceny is used when talking about stealing someone's property in regards to the law. If you illegally download music or plagiarize a text, that may be theft, but it is not larceny because there was no physical property involved. If you take a friend's yoyo and don't give it back, it's stealing — unless your friend calls the police and has you arrested on charges of larceny.