In computer-speak, this term is used interchangeably with CPU. It is frequently described as the brain of a computer because the processor controls the central processing of data in personal computers (PCs), servers, workstations, and other devices.
Until 2005, most consumer computers had a single processor. Now it's common to find them with so-called dual cores, which means two processors packaged into one chip. Two cores won't make your word-processing or email go any faster, but they do potentially give you more horsepower for heavy-duty tasks like gaming or video editing (provided you have the software that sends some work to each core). Intel first called their dual-core chip the "Core Duo;" now there's a second-generation known as the "Core 2 Duo." There are also single-core Intel processors called "Core Solo." For laptops, see PC Card.