Squishing a bit of data down so that it takes up less space than the original. There are two kinds of compression:
*Lossy compression – you remove some of the data (sometimes there might be a pattern, so you remove the repeating bit and say that it repeats)
*Lossless compression – stores a map of the repeating bits, so that you do not remove any data in the compression

A Zip file is one type of file that can contain several other files that have been compressed together.