This means 'Category 5' cable.
CAT 5 cable is designed for use in computer networks running up to 100Mb/s.
It is made up of a number of smaller wires twisted together in groups of 2. These are called 'twisted pairs'. The twisted pairs are held together by a plastic sheath to form the CAT 5 cable.
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: CAT 5