The crop factor is often the ratio of the dimensions of a camera's imaging area compared to a reference format. Generally speaking Crop Factor is applied to digital cameras, relative to the old 35 mm film format as a reference point.
In simple terms some sensors give you more (or less) zoom all else equal.
In other words with the same lens and body you may get a 1.5x zoom if you use an APSC sensor vs on 35mm.
Here is a video on this topic:
video by Tony Northrup