What does it mean to have a "body for days"?

It's that or "a body that lasts for days" I think. I've heard that a few times and don't really understand what it means since the only times I heard them used were very different I recall.

It depends on the context it's used in. Examples:

A fast weight loss program will give you a body for days, then it's back to the same old you.

The killer remained in the house with the body for days.

The imitation tattoo remained on my body for days.