In modern networking, there are multiple media types including various types of Ethernet, Fiber Optic and Coax cabling. The Small Form Factor (SFP) transceiver is a standards-based device that is used to allow different physical network media connections to network devices such as switches. SFP has a standard mechanical and electrical interface for interchangeably.
Many applications of the SFP are for fiber-optic network connections that provide electrical separation or long distance transmission needs. In most home networking situations, we do not see any use of SFP devices. There is a growing use case for fiber-optic networking cabling to provide electrical noise isolation. I will expand on this in a later blog post.
For reference here is the Wikipedia entry for SFP: