BPM stands for "Beats per minute" and is a measure of the tempo of a song. The higher the BPM is, the faster the tempo is.
Knowing the BPM of songs is crucial if you are a DJ and want to mix different songs together. By mixing songs of the same BPM you can create flawless transitions.
It is possible to add metadata to your audio files that shows the BPM of the track. This is useful for music library softwares. This tool allows you to automatically save the detected BPM as metadata. This feature does not work on WAV files.