AAC or Advanced Audio Coding is an audio file format with losses. It was designed in 1997. as an MP3 successor with improved encoding quality. Its main advantage and difference from MP3 is a great efficiency of encoding at both constant and variable bitrates.
WAV is a container format for storing a record of a digitized audio stream without any compression. This format was developed by IBM and Microsoft in 1991 and was used in all versions of Windows. As the format uses audio streams without any compression, the files become very large in this format.