Definition of sector

1. particular group of stocks, usually found in one industry. securities analysts often follow a particular sector of the stock market, such as airline or chemical stocks.
2. part of the economy, as in private sector or public sector.
3. division of a computer floppy disk.

part of a track on a disk. For example, the original IBM PC diskette system partitions the diskette into 40 circular tracks with each track having 8 sectors.