Small Form-factor Pluggable is a compact, hot-pluggable network interface module format used for both telecommunication and data communications applications. An SFP interface on networking hardware is
Small Form-factor Pluggable connected to a pair of fiber-optic cables
A 10 Gigabit Ethernet XFP transceiver, top, and a SFP+ transceiver, bottom
QSFP+ 40 Gb transceiver
40 Gbit QSFP+ transceiver showing the optical fibre connection