Resampling? little confused, any help would be greatly appreciated

Im studying for my GIS exam and there's one thing that's confusing me a bit. The two questions are, 1)What is resampling?2) When is resampling used? Why?

Ive gotten conflicting answers. Ive found that to resample is to change cell size, increasing the cell size. Ive also found that resampling is "The process of interpolating new cell values when transforming rasters to a new coordinate space or cell size."

Then for question two when to use it i found, "After a Transformation to new coordinates or cell size" which would seem to conflict with the answer for what resample is which was a change in cell size.

If anyone could clarify this for me it would be greatly appreciated.

thanks