LAN

Most Ethernet cards come in two configurations -- 10 megabits a second, or combination cards that run at either 10 or 100 megabits, known as Fast Ethernet. Cable and ADSL connections usually operate well below 10 megabits, so the minimum card is fine here. However, if you are considering using Ethernet to create a home network, opt for the faster cards, which will make transferring files and data between your home PCs much snappier.

Also now have 10/100/1000 Gigabit Ethernet Cards

Three speeds: 10Mbps (10Base-T), 100Mbps (100Base-Tx) and 1000Mbps (1000Base-T)

Here is a link that explains the whole range including wireless, satellite etc OCx
( Optical Fibre Levels )

http://whatis.techtarget.com/definition/0,,sid9_gci214198,00.html