An octave is a special kind of musical interval that happens when you play or sing two notes that are very similar to each other. They are so similar that they almost sound like the same note, but one is higher than the other. Normally an octave distance sits between two notes which are exactly 12 semitones apart from each other.
But sometimes, people want to change the way an octave sounds. They change it by stretching it, which means they make it a little bit bigger. It's like when you pull on a rubber band, it gets longer and looser. The stretched octave sounds a little different than a regular octave because the two notes that create it are just a tiny bit farther apart than usual.
Musicians might stretch an octave to create a unique sound or feeling in their music. It's like adding a special seasoning to your favorite dish to make it taste even better. Some people might like the sound of a stretched octave more than a regular octave, while others might not even be able to tell the difference between the two.
Overall, stretching an octave is just a way to add some variety and spice to music. It's a way to make something that might sound normal and ordinary, just a little bit more fun and interesting!