LLM stands for Master of Laws, an advanced legal degree. In the American judicial system, the LLM does not entitle recipients to take the bar exam or practice law; those privileges require a Juris Doctor (JD) degree. Oddly enough, the LLM ranks higher than the JD, even though the former is a master's and the latter is a doctorate. (According to a cynical lawyer friend, the LLM was originally the highest law degree until a bunch of lawyers decided that they needed a doctorate too, just like the physicians and the professors out there.)

LLM programs generally allow students to specialize in a particular area of law, such as taxation, international law, business, health policy, and so on. They usually require one school year; some programs require a thesis. Also, Sekicho tells me that foreign lawyers often get an LLM to practice in the US.