How many pixels a Kernel is moved before being applied is called the stride which in 2D can be denoted for the stride in the x-axis and in the y-axis.
The value of the stride is a design choice that influences the dimension of the output, as the convolution will have approximately elements for a picture of pixels. The word approximately is used because the convolution stops at the edge of the image.
One can however pad the image with extra pixels, which are zeroes of copies of edge pixels, so that the kernel is applied exactly .