Integer and subpixel shift

I wanted to know what integer shift is?

And what is the difference between integer and subpixel shifts in the image processing?

Assuming you have seen this in an image processing literature, then no, it does not mean what it generally means in computer science.

The likely thing is that you have seen this somewhere where the images are "shifted". The shift (moving a pixel to a different location) can be done by moving the entire pixel to the location of the adjacent pixel, being this an integer movement, because you have moved it by 1 pixel. Or it can be done by moving the pixel by less than this (probably using interpolation to generate a new image). If you do this, you are moving the image in subpixel (less than pixel) motion.

In the following diagram, images N1-4 have subpixel sifts, as each square (pixel) is far from the others by non-integer distances