Film and television show movement by displaying a sequence of images. Each image is a Frame. The number of frames every second is the frame rate.

Film in cinemas is typically 724 frames per second. PAL, used in most countries is 25 frames per second. NTSC, the US standard us 30 frames per second. These are the three main ones. 

When televisions were first invented, they relied on an electron beam scanning line by line, from top to bottom. In those days a TV was made up of 768 lines. The problem was than when just over half the lines had been drawn, the top was starting to fade. To fix this, the engineers scanned every other  line then the remaining lines after that. Each frame was therefore made up of two 'fields', so 25 FOS but actually 50 fields per second.

The reason most of the world uses PAL at 50 fields per second is because we have electricity running at 50 hz. Each hertz corresponds to one field. The USA uses 60 fields per second and has 60 hz power. The power frequency was the original timing mechanism.