What is the difference between prison and jail?

In the United States, jails are generally run by cities or counties, where prisons are run by states or the federal government.

Jails hold people who are awaiting trial, or for those serving sentences of less than one year. Most of those sentences will be for misdemeanors, lesser crimes than felonies. Prisons are for people serving sentences for felonies, which are for more than one year.

Jails are usually fairly low-level in terms of amenities. It's unlikely there will be any education or rehabilitation programs. They are often crowded, at or exceeding design capacity. Larger jails will have a medical section for prisoners requiring special care for illness or injuries. If the situation requires more care than the jail can manage, the inmate is taken to a hospital under guard, or just released from custody if the charge is relatively minor. If the inmate remains in custody while in the hospital, the county is on the hook for all costs of treatment.

There isn't much for inmates to do in jail. If they're lucky, they have TV to watch or a small library to borrow books from. More often, they pass the time by talking, or playing cards or board games.

Meals tend to be the high point of the day, and the bar for that is set pretty low. The meals are usually prepared by inmate "trustys" (inmates who are considered low-risk and perform work inside and outside the jail), and seldom have much experience in culinary arts. The kitchen is overseen by a full-time cook.

Large jails have to carefully segregate prisoners according to gang affiliations. Every gang has its rival gang, and putting a gang member in custody with his rival means that one of them is likely to get killed, or at least severely injured. They regard it an obligation to kill every member of the rival gang, at any opportunity.

Jails can be large (the LA County Sheriff's Department runs the largest jail system in the world, with a daily inmate census of around 22,000). Most jails have capacities of fewer than 10 to several hundred inmates.

Prisons generally have hundreds, occasionally thousands, of inmates. They vary between minimum security to super-maximum security. In minimum security, the prison may resemble an apartment building or summer camp. There are usually no fences or guards carrying firearms, and the inmates can (and occasionally do) walk away unnoticed. At a supermax prison, inmates are generally housed in single cells where they spend a substantial amount of the day, possibly with some co-mingling in a common area where 30 or 40 inmates have access. They are usually fed within these housing units, so they don't move through the rest of the prison very often.

There aren't many supermax prisons. They are personnel-intensive and therefore expensive to operate. They are reserved for only the most violent and high-security prisoners, and even the tougher inmates are cowed when told they are going there. I've read that a few inmates are held in Hannibal Lecter-style cells, with plexiglas walls in front and with lights on 24 hours per day.

Most prisons have some level of educational or rehabilitation programs, vocational training programs, or prison industries where the inmates make everything from license plates to bullet-proof vests. If you've gone to a public school or college, you've probably sat in a chair, written on a desk, or taken a book from a shelf made inside a prison.

These diversion programs in prisons tend to be outdated or inadequate. Funding of prison programs is seldom a priority in government. Too many citizens would rather lock offenders away and forget about them. The rehabilitation programs, however well-managed or -funded, tend not to be very effective. A few people reform because or through the influence of them, but recidivism rates are always high, especially if you look beyond the first year or two after release.

Most jails and prisons have segregation units, where inmates are housed in solitary confinement for disciplinary or protective reasons. In "seg," inmates are housed in windowless single cells for up to 23 hours per day, and the remaining hour may be spent in a room or cage not much bigger than the cell. The practice of holding inmates in solitary confinement for long periods is psychologically punishing, and is coming under increasingly harsh criticism. It may eventually come to an end, but whatever replaces it as a measure to get inmate compliance with institutional rules may be something worse.