DB9 connector, a common type of electrical connector. The term \u201cDB9\u201d refers to a common connector type, one of the D-Subminiature or D-Sub types of connectors. DB9 has the smallest \u201cfootprint\u201d of the D-Subminiature connectors, and houses 9 pins (for the male connector) or 9 holes (for the female connector).