It comes from the idea that certain products are "locked down" to where you cannot do anything else with it but what the manufacturer provisions. Jailbreaking m

It comes from the idea that certain products are "locked down" to where you cannot do anything else with it but what the manufacturer provisions. Jailbreaking means you gain complete control over the device, so that you can do anything else you want with it. I believe the term either originally came from, or was at least popularized by people wanting to escape Apple's "walled garden", which is also viewed by some as a jail.