Lets consider a 1D Fourier transform example:
Consider a complicated sound such as the noise of a car horn. We can describe this sound in two related ways:
Similarly brightness along a line can be recorded as a set of values measured at equally spaced distances apart, or equivalently, at a set of spatial frequency values.
Each of these frequency values is referred to as a frequency component.
An image is a two-dimensional array of pixel measurements on a uniform grid.
This information be described in terms of a two-dimensional grid of spatial frequencies.
A given frequency component now specifies what contribution is made by data which is changing with specified x and y direction spatial frequencies.