What is the transparent plastic cap on the back of an SLR camera lens called?

I have a Nikon D60 and the plastic cap came off of the body of the lens. What is the correct name of this so that I can purchase another one?

Body caps and lens caps. The body gets 1, to cover the mirror. Each lens gets 2, one on each end. If you search ebay for D60 cap you should get OEM replacements.

Rear cap.http://www.amazon.com/Nikon-LF-4-Rear-Lens-Cap/dp/B0045TYDNC/ The cap for the body is called a body cap.

Rear lens cap.

By the way they sometimes come in black too.