This adapter breaks out connections from a 15-pin D-subminiature connector (popularly called DB15, but more properly DA-15) to a set of screw terminals, making accessing those pins easier during prototyping. The adapter is designed specifically to work with the MCP Advanced Motor Controllers that feature a DB15 connector: the MCP233, MCP236, MCP263, and MCP266. However, it could also be used as a generic breakout board for other hardware that uses the same connector, like old computer joysticks or MIDI devices (where it is called a game port).
The adapter includes a plastic housing, connector screws, and a small clip that can be screwed into the housing for wire strain relief.