Kata (型 or 形) has no real translation into English but loosely means forms. Kata is often referred to as the heart of karate and is largely responsible for the art's survival.
Kata contains all the techniques, ideas and strategies that are needed for combat.
In Goju-Ryu there are twelve traditional katas and as a student progresses they learn more advanced kata.
A kata cannot be said to have been 'learnt' until the student can apply any part of that kata to any given situation at will. Therefore it can take years to fully 'know' a particular kata.