Small Computer System Interface (SCSI) is a set of standards for physically connecting and transferring data between computers and peripheral devices.
The physical SCSI interfaces - originally used to attach peripherals like disks, scanners and tape drives - have mostly been superseded by sas and usb.
The SCSI command set that was originally defined for (parallel) SCSI buses has been carried forward with minimal change for use with fibre-channel, iscsi, Serial Attached SCSI sas, and other transport layers.