Frame rate, which is the speed at which a camera takes pictures, is usually defined by the number of images taken per second. It is measured in FPS, i.e. Frame per Second. 

Line rate, in fact, is a special frame rate: for only a few lines of pixels of CMOS, its photo speed is very fast, can reach tens of thousands of pictures per second - hundreds 

of thousands of pictures, said out of the number of many, but because the picture taken, close to a line, can not be used directly, in order to avoid misunderstanding, it is not called 

the frame rate, but called line rate.

When it comes to frequency, the first thing that comes to mind is the wave, the period. If you imagine the blue line in the picture below (a line image from a line scan camera) as a wave peak, 

the number of times the blue line appears in a second is the frequency of the wave.

This is also the origin of the word "line rate".

The line frequency determines how many lines of "line images" the line camera can take per second.

For example, a 4K line scan camera with a line rate of 16K, assuming it has only 1 line, will produce a 4096*16000 resolution image after 1 second.