What does "creasing" mean?

Question

most ppl use a eyeshadow base to "avoid creasing" what does that mean

Answer 1

where you can see little lines where the eyeshadow has come of  

Answer 2

When you close your eyes, your eyelid is pulled tight and smooth, when you open them the skin folds and creases. If you do not use a base, the eye makeup will sometimes build up in the creases and you will have thick lines of make up rather than a smooth all over finish.

Answer 3

to avoid wrinkling on your face.

Answer 4

its when you put eyeshadow on your eyes and a couple hours later it doesnt look like a smooth color belnd anymore when you close your eyes it will look like the shadow clumped together in little lines