Occam's Razor refers to a "principle" used in science to help choose between competing theories explaining some phenomenon.
If two theories seem equally compelling in their elucidation and explanation of a phenomenon, Occam's Razor suggests that the simpler of the two explanations be preferred. By simpler is meant that explanation which has the least superfluous explanatory aspects to it.
A good example is the comparison made between Copernicus' Heliocentric Model of the Solar System and Ptolemy's Geocentric Model of the Solar System. Both "worked", in the sense that both made equally accurate predictions, but comparatively speaking, the Geocentric Model had so many "moving parts" and non-scientific assumptions about planetary motion as to be comparatively absurd. Occam's Razor would tell us to prefer the Heliocentric Model, because the motions of the planets are comparatively much simpler to understand.
Occam's Razor is not a rigid principle but a suggested style of thinking. Einstein clarified this point by saying that "Everything should be made as simple as possible, but not simpler."