568B

568B is a wiring standard setup by the TIA/EIA. Part of it determines the order in which you place individual wires into an RJ45 jack--an RJ45 looks just like a telephone jack (RJ11), only bigger--when constructing a twisted pair cable. When you get a roll of networking cable (as opposed to individual cables that are allready finished), it doesn't have jacks on each end. So, you cut off the amount that want, order the pairs of wires according to what type of cable you want, and crimp them into an RJ45 jack to make the cable usable.

For 568B you put the pairs in this order (make sure the RJ45 jack is facing downward):

White/Orange   Orange   White/Green   Blue   White/Blue   Green   White/Brown   Brown

When it says White/Orange or White/Green that means the wire is White with a green or orange stripe.

The reason why the 568B order is used is because of the signalling requirements of various layer 1 networking protocols that travel over these cables.

For instance, twisted-pair ethernet uses pairs 1/2 and 3/6 for transmission and reception, so making sure that 1/2 is one twisted pair and 3/6 is another, you reduce crosstalk in the cable.

Some telco protocols like ISDN use pins 4 and 5 in the cable; this is why 4/5 is a twisted pair in EIA/TIA-568B. The goal is to make an EIA/TIA568B patch cable usable for as many different communications standards as possible, providing twisted pair paths for all signalling as often as possible.