Time-stretching is the process of changing the speed or duration of an audio signal without changing its pitch. In other words, it allows you to make an audio recording shorter or longer, while keeping the pitch of the sound the same.
For example, if you were to time-stretch a song, you could make it play at a slower tempo without changing the pitch of the vocals or instruments. Or, you could speed up a recording without making the vocals or instruments sound higher in pitch.
Time-stretching is a useful tool for when you want to manipulate the timing of an audio recording. It can be used to match the tempo of different parts of a song, to create new arrangements or remixes, or to correct timing issues in a recording.