What is the difference between Filters and Windowing?
Filters and windows complement each other, in a way. This is due to the convolutional lemma of the fourier transform.

Let me expand on that. A filter would be a convolution of a signal with another. In a technical sense, a window has a fixed (supposedly short) size and is seen as "cutting out" a short part of the signal. Often, a DFT would follow.

In the fourier domain, convolution and point-wise multiplication trade places, so a convolution in the time domain is a pw. multiplication in the fourier domain and vice-versa.

A filter scales the spectrum with a known frequency response. A window will filter the spectrum instead.

Filters and window functions often (but not always) have different design goals. For example, in a filter you would have rather large bandwidths. Windows percieved as useful have a small bandwidth (often, just a few samples). You can talk about both kinds in the same terms, you just have to remember that both are used in different contexts.