The frame rate is the number of images distributed in one second. A "50p" or "XXXXp50" video stream contains 50 images per second (frames per second, fps). With interlaced video the 50 frames are actually only half frames with every alternative number of lines.
One second equals 1000 msec, a video stream with a frame rate of 50 fps carries five images in 100 msec (a 1/10th of one second).

50 progressive frames per second (Europe) each frame containing a full image	50 interlaced frames per second (Europe) each frame containing a half image with every second line
60 progressive frames per second (US) each frame containing a full image	60 interlaced frames per second (US) each frame containing a half image with every second line
25 progressive frames per second (Europe) each frame containing a full image	24 interlaced frames per second (Movie Format) each frame containing a full image
24 movie frames with a double shutter to create 48 images per second	24 movie frames with a triple shutter to create 72 images per second

24 movie frames with a double shutter to create 48 images per second	24 movie frames with a triple shutter to create 72 images per second

Movies were and are shot and displayed in the frame rate of 24 frames per second. This is based on the development of film technology over time. As soon as movies are transferred to video frame rate conversion must be considered. For PAL with a frame rate of 50 fps the regular method is the "PAL speedup": the 24 fps movie is transferred to the PAL medium with an upspeed of 4.167 percent, resulting in a frame rate of 25 full images er second, resulting in an interlaced picture with the frame rate of 50 fps. The slight upspeed is normally not realized viewing a movie, but the pitch change could be a larger problem. To sole this ofen pitchbending is used to transfer the audio back to the corect pitch while speeded up.
With NTSC video with a frame rate of 30 / 60 fps the speedup dosn't work, the movie's speed would be visibly too fast and audio re-pitching would be difficult. Since 60 and 24 are no integer numbers, an uneven adjustment is necessary. The regular method is a 3:2 pulldown, there from one full image (progressive) alternatively two and three half images (interlaced) are created. This method has some serious drawbacks because the interlaced half images are not always corresponding correctly to each other. The so-called "Judder" is the result: camera moves will be displayed with an ofen visible shaking image.
Another problem with the 3:2 pulldown is that the interlaced video cannot be correctly put back into a progressive video (half frames don't fit). With a 60 fps display the best method to get a progressive video is to first re-create the 24 full frames. These 24 full frames are then displayed in an 3:2 sequence to get the 60 full images by playing alternatively one frame three times (as a full progressive image) and one next frame two times (also as a full progressive image).

Movies on BlueRay Discs are normally encoded at the original 24 frames per second. With a good display it should be possible to present movies in pefect quality. But with 60 frames per second as the standard frame rate for modern flat displays the above issue must be solved too. Movies can be displayed with the 3:2 pulldown.
LCD displays show the image as long as it is active without a short space between. 24 images per second work in cinema only because the image is interrupted by a shutter wheel that is rotating in front of the lens, 'cutting' the 24 images into 48 (2 times) or 72 (three times). With each blank phase the eye (and the brain) simulate the missing image path and a smooth moving image is seen. With a LCD screen without blanks the 3 and the 2 partial images of the 3:2 pulldown are seen as static images and the change between the images is seen as a sudden change. With a moving camera image here also a distorted flickering image will be seen.
A solution is the artificial calculation of the 'missing' images between to images to create a smooth move from one image to the next. This works well but often the created image looks artficial (the so-called 'soap effect', based on the visual impression of the cheep production technique fo Soap Opera productions, lokng as if the persons are disconnected from the background image). Only some of the consumer displays (tv sets) are able to display the 24 fps in a good way.