SFP stands for "small form-factor pluggable" and is a
hot-swappable input/output device that plugs into a Gigabit
Ethernet port or slot, linking the port with the network.
SFPs can be used and interchanged on a wide variety of products
and can be interchanged in combinations of 1000BASE-SX,
1000BASE-LX/LH, 1000BASE-ZX, or 1000BASE-BX10-D/U on a port-by-port
basis.
You can use them for Gigabit Ethernet or Fibre Channel
applications. They provide a flexible and cost-effective solution
for enterprise networks, data centers, etc.