Waveform Audio File Format (WAV) is an audio file format in other words helping to visualize the sound in the clip by showing the signal levels. Premiere can show a waveform in audio tracks in the Timeline and in a separate Clip window when you open an audio clip.
It is considered a "first generation" format without compression, except for some manipulations to store the audio digitally, resulting in larger sizes compared to formats such as MP3 and WMA. This standard was developed by IBM and Microsoft for storing an audio bitstream on PCs.
It stores raw audio that doesn't need special encoders/decoders to use it, making it a very good standard for interchange with different platforms or operating systems such as Windows, Mac and Unix.
Although a waveform audio file may contain compressed audio, uncompressed audio using the linear pulse code modulation (LPCM) format is most common.