What is End Effect in signal processing?

What does End Effect in signal processing basically means? I would like to see some reference book or papers if you suggest me.
Thanks

The end effect refers to where many filters and similar processes produce spurious results at the ends of the dataset.

There are several reasons why this can occur. The most common one is when using moving window based filters the filter is not well defined at the boundary. For example consider a filter with a window of size 3. At your first data point ($n=1$) this filter is not well defined as $n=0$ does not exist. In order to calculate a value at this point the most common approach is to pad your data (often with zeros) to extend the width. As this is not real data it will skew the results for these points.

I can't find much literature on it. The book Biosignal and Medical Image Processing has a little bit.