English mathematician George Boole (1815-64) founded a field of mathematical and philosophical study called symbolic logic. His name is now used most often to describe a subset of symbolic logic: constructing database queries.
Whenever you see a Web search tool or database query system that allows you to use AND, OR, and NOT to hone your search, the chances are it uses Boolean techniques. The most common Boolean operators are AND (you're looking for all terms), OR (you're looking for at least one of the terms), and NOT (you're excluding a term). You'll always see the operators referred to in uppercase letters, although you usually don't need to enter them that way to make a Boolean search work properly.
Also, the Boolean operator AND doesn't work like a normal English and. For example, a Boolean search through a database of rock musicians for members of the Beatles AND Wings would turn up only Paul McCartney. For details on how to construct Boolean queries, read CNET's Boolean search primer.
See also: Boolean operator