sd originates from the driver
sd-mod. It literally stands for scsi disk.
The reason (S)ATA disks are also listed as SCSI disks is, SCSI commands pretty much provides a superset of features that can be provided by ATA commands, therefore modern systems (including Windows, AFAIK) will have an implementation of SCSI-ATA Translation Layer (SATL) in the system (in Linux it is provided by the
libata driver) to talk to the (S)ATA disks, while the upper layer of the system can be generalized.
As you may not aware of, USB drives "speaks" SCSI (i.e. takes and responds to SCSI commands), no matter if it supports the USB Attached SCSI Protocol or not. Also, most of the USB HDDs/SSDs are SATA disks bridged to USB. For those the bridge provides the SATL, but not the operating system.