It is an Options Card.

Straight from the F1 Help file:

An Options Card provides onboard Digital Signal Processors (DSPs). Each of the DSPs installed on the OPC (up to four) may be configured as one of several available resources. Caller information features require OPC programming to ensure that resources are available to support the features. Caller ID (CLIP in Europe) uses Caller ID (CLIP) receivers (available for US systems only) and DID/ANI (or DDI/ANI for Europe) uses DTMF receivers. The Options Card can also be specified as having a Voice Processing Unit (OPC to AIC) connection to support additional ports.