The SCSI (Small Computer System Interface) was used to physically connect two computers to peripheral devices and transfer data between them. SCSI was used to connect hard disk drives, tape drives, scanners, CD drives, and other devices. SCSI is pronounced “scuzzy.”
The Apple SCSI Active Terminator was used to allow “active termination” in a chain of SCSI devices. Active Termination is defined as an advanced form of terminating SCSI cables that controls “the impedance at the end of the SCSI bus by using a voltage regulator, not just the power supplied by the interface card” (myoldmac.com).
Although different SCSI interfaces were available, this terminator uses the original parallel SCSI interface.