Jails do hold long term prisoners, and prisons get pre-trial prisoners too.
There’s literally a market for jail beds. So prisoners are often sent where there’s an open spot, with little distinction between “short term” and “long term”.
A better distinction is that jails are run by a law enforcement agency, while prisons are not.
In practice, the distinction is overblown.
Jails do hold long term prisoners, and prisons get pre-trial prisoners too.
There’s literally a market for jail beds. So prisoners are often sent where there’s an open spot, with little distinction between “short term” and “long term”.
A better distinction is that jails are run by a law enforcement agency, while prisons are not.