What does OpenCV's cvAcc() do?

Could someone please explains in simple, non-technical and non-mathematical terms what exactly does cvAcc do? I read that it it "accumulates", but have no idea what accumulates mean开发者_JAVA百科s.

Thanks

Accumulation is the result of adding (or summing). It's kind of what the += does in C/C++. So

cvAcc(image, accumulation, mask);

Is like

accumulation += image; // with the mask applied so only a region might be affected