Frame Rate, also called as Refresh Rate defines the rate/frequency at which frames(picture) is displayed on the screen per second (fps).
Common frame rates are 60 fps (NTSC video), 50 fps (PAL video), or 24 fps (film and movies).
Modern display technologies, including LCDs. and the iPhone’s screen refreshes at 60 fps (refresh rate). If you are developing a game for iPhone the frame rate should be close to 60fps for smooth animation.