You bought a new baseball hat. Your friend tries it on, just for fun, but laughs because it's much too small. You point out the velcro in the back.
Say this if it’s possible to change the fit of something.
For example, imagine that you’re trying on a ring at a jewelry store, but it’s a little too small for your finger. The saleswoman takes the ring and shows you that it can be pulled apart to become larger:
Here you go. It’s adjustable.
Other things that are "adjustable" include settings on a machine, like the volume, brightness, or color balance of a TV.
In general, words that end in "-able" mean "able to be ___ed". Some other examples: