You can tell the OP hasn't been in the 'system' he still calls it 'jail'.

Jail is what petty theifs go to who don't have bail in the county level.

CRIMINALS do numbers as in YEARS

You do your bit in the joint or PRISON

Fellow inmates speak like this

So what's your number down the road

Or what's your number up state

NUMBER IS HOW MANY YEARS you gonna do in the REAL CRIMINAL UNIVERSITY

PRISON

haha

If you deal with criminals like CRIMINAL LAWYERS do you learn the lingo

You guys wouldn't last 3 minutes in the yard without having some punk take all your stuff.

haha

Now if you have a few belts in martial arts, you the king of the yard since you're what they call a JAW BREAKER

That means one strike fist or foot you take jaws sideways and the dude is WIRED for a bit

JAIL

JAIL is for pussies

CRIMINALS DO NUMBERS

It's called PRISON