This is a 3.5mm female to terminal block connector. This connector is suitable to make your own cable when you need a 3.5mm female connector and do not want to solder a connector.The tip of a 3.5mm male connector corresponds to the "+" on this connector.
The middle ring on a 3.5mm male connector corresponds to the "-" on this connector.
The sleeve on a 3.5mm male connector corresponds to the "ground" screw terminal on this connector.
This connector has a Terminal Block with screw terminals for you to insert the corresponding wires for different applications, such as stereo audio or infra-red signals.
The Terminal Block is labelled "+", "-", and has a symbol for "ground."