They are generally the same thing. The only real difference is that jail can be very small, perhaps a single room. Prison almost always means an entire building, or most of one.

A jail is a local lock-up for holding people awaiting local court appearances or serving time on local misdemeanor charges or sentences of less than one year. The simplest explanation is that a jail is allowed to hold prisoners for up to one year. Any sentence over a year must be served in a prison. It used to be that jails were only holding facilities and prisons were "reformatories" but now even jails are considered reformatories in many places. The most notable difference is that prison inmates have been tried and convicted of crimes, while those in jail may be waiting for a trial. A prison is under the jurisdiction of either federal or state, while the jail holds people accused under federal, state, county and/or city laws. A jail holds inmates from two days to a year only.

There is not a major difference between jail and prison for a common man, but in the eyes of a lawyer two of them are totally different. a jail is used for short term stay whereas a prison is for a long term stays. Jail is used by local jurisdictions in countries and cities, whereas prison is administered by the state or federal government. People convicted for a short sentence or trials, detainees, suspicious people under trials are kept under jail. Jail has fewer amenities for its convicts as compared to a prison. It only provides the basic necessities of food, housing and safety to the prisoners. Jails operate camps, vocational trainings and other work release programs for the prisoners. Jails are within the country where the individual is arrested. Typically they are intended to hold persons for less than one year. Whereas the prison is for long term convicts who have been tried and convicted of crime. It is normally located away from the place of arrest. There are few prisons as compared to jails. Prison has a tight security and more amenities for the people. It provides the basic necessities as well as exercise areas, common areas for socializing and educational areas too. The area coverage is also more than the jail. Prison has a specially trained staff and a board of governor to oversee the prison management. A prison is divided on the basis of the type of crime, a person commits and he is placed accordingly, unlike in jail. Prison has work release centers, community restitution centers and other entertainment facilities for the prisoners. This prison system is a type of correction system arranged by the province or a state for the convicts. http://www.differencebetween.net/miscellaneous/difference-between-jail-and-prison/

Maybe they are synonyms :)