In music, a variation is a process that

produce multiple musical phases by making

modifiacations to a "theme".

It is the same for an evolutive pictorial work whose variations can be of different natures. 
They can be:

Methodical

The theme undergoes modifications such that it is more or less recognizable in different intervals

Rhythmic.

The projection times of the visuals and their transitions are modified in order to make the work dynamic.

Harmonic.

The tone and harmony of the colors corresponding to the theme are modified more or less sensitively.

These various modes of variation can be combined with each other, the initial theme then becoming

almost unrecognizable