https://www.busterbirch.co.uk/rhythmchangessoloing

An enclosure is a way to decorate and embellish chord tones. You can use it on any of the chord tones. Essentially, what you're doing is targeting one of the chord tones. You play a note above it and a note below it, and then hit the chord tone. It's like making a little sandwich with the chord tone in the middle. There are many variations you can use, but a popular and common one to start with is playing a scale tone above, a semitone below, and then landing on the chord tone.

In this example from my book "The Rhythm Changes Soloing," I refer to enclosures as EA for enclosure above and EB for enclosure below. The exercises in the book help you to develop some bebop language by embellishing the chord tones and arpeggios.

The first exercise is all just eighth notes, like an arpeggio exercise. In the second exercise, we take away a few notes to create more angular bebop-sounding lines. Remember, these are just exercises to work with one ingredient at a time.

It's important to practice and learn in a very controlled way, especially when starting out. Enclosures are really useful and can be applied in various situations. It's a classic bebop and modern jazz approach to add a certain sound to your playing.