This type of connector got its name from the Centronics Corporation, a manufacturer based in Nashua, New Hampshire. Back in the 1970s, Centronics made printers for use with computers. As computers and attached printers became more popular, the connector that they used became the de facto industry standard. The Centronics Corporation was purchased by Genicom (now TallyGenicom) in the 1980’s, but their name lives on in this connector. 
 
The Centronics connector has a plastic bar in the center of the connector body that holds the contact pins. The body of the connector is often blue in color.

Centronics 36: The 36-pin connector is often used for parallel applications, especially for printers. It is also referred to as an IEEE-1284 Type B connector. The Centronics 36-pin connector is arranged in two rows of pins, each with 18 contacts. The connector is held in place by bail locks. Printer Cables, IEEE 1284 Printer Cables, Adapters, Gender Changers

Micro Centronics 36: This connector can described more accurately as a mini-D ribbon (MDR) connector. It looks very similar to the Centronics 36-pin, but is about half the size. This interface is also called an IEEE-1284 Type C connector, and is commonly found on parallel multifunction (printer/scanner/copier/fax) devices. This connector is held in place by squeeze latches. Cables

Centronics 50: The Centronics 50 connector has 50 pins arranged in two rows—25 on the top, and 25 on the bottom. This connector is most often used by older SCSI-1 devices (scanners, storage devices, etc.). The Centronics 50 connector is held in place by bail locks. A slight variant of the Centronics 50 connector is used in voice/data applications. This variant is commonly called a Telco connector. Cables, Terminators, Adapters, Gender Changers