A cable is, essentially, a group of stitches that is divided into two smaller group. Either the first group crosses in front of the 2nd group to create a Cable Left (aka Cable Front) or the first group crosses behind the 2nd group to create a Cable Right (aka Cable Back)
CABLE 4 LEFT
The first technique symbol on the key to the left is the Cable 4 left. This is a cable made up of FOUR stitches.