Codabar (or "Code-a-bar") is one of the older bar code formats (or symbologies), dating to 1972, when it was developed by Pitney-Bowes. It was designed to be printable on dot-matrix printers and typewriter-like impact printers. This format has been used in libraries, FedEx airbills, and blood banks.
Symbols consist of a set of 4 bars and 3 spaces, each of which can be wide or narrow, separated by narrow spaces from adjacent symbols. The character set comprises 20 different characters, of which 12 are the "basic" set (numbers, dash, and $) and are encoded in combinations which include one wide bar and one wide space, and 4 (:/+.) have 3 wide bars with no wide spaces, and 4 start/stop symbols have one wide bar and two wide spaces.