Perspective – The mathematical rules which define how a 3D scene is mapped to a 2D image. The way objects appear smaller when further away.

The following should help you remember what perspective is:

She has perfectly ugly magnifying spectacles but she can give (perspective) you brilliant mathematical rules.

To remember perspective is also the way objects appear smaller when further away, look at the following image:

When people walk away from her, her perfect spectacles give (perspective) her very clear vision but people do look a lot smaller further away.