Movies are shot at 24 frames per second, but until now have had to be speeded up a bit to suit the frame-rate of TVs, which in the PAL system is 25fps. This gives a slight upward pitch-shift in the soundtrack, and can cause slightly juddery movement, most obvious in slow panning shots, which can seem to jerk a little, thanks to the 'pulldown' system used to turn 24 frames every second into 25.
Now, with the arrival of Blu-ray, films can be delivered on disc at their original frame rate - cue lots of 'as the director intended' razzamatazz - but the TV through which you play such discs needs to be able to handle the 24fps frame rate.
50Hz is the European PAL TV standard - ie 25 frames a second, composed of 50 fields, or half frames, in the interlaced TV standard. Basically the TV writes a field made up of every odd line of picture info, followed by another made up of every even line, and leaves image retention in your brain to do the rest.
100Hz scans each line twice - that's in very simple terms! The jury's still out on the benefits of 100Hz over 50Hz for certain types of programming, even though this has been available for yonks. It varies according to the manifacturer's implementation - some users prefer 100Hz, while others are happier with 50Hz.
However, of course 24 doesn't go into either 50 or 100 exactly, so TVs able to show 24fps need to be able to write at a multiple of 24, usually meaning 48Hz or 96Hz.