How to Measure Oven to Buy New One
The niche width is usually the width of the opening the oven will fit into.  If you have a niche width 22", the oven you purchase would have to be smaller so it fits into the cabinet/space. The oven protruding width = 24" would be the width of the oven door which is usually 2" wider than the oven.

Oven depth is how far the oven will stick out from the wall. A common notation would be: oven depth = 22", protruding depth = 24". The extra two inches is for the handles and knobs that stick out from the front. Hope this helps.