In Pennsylvania DUI stands for Driving Under the Influence. In some states its call DWI, which stands for Driving While Imbibing. In order to be found guilty the Commonwealth must prove both that you were driving the car and that you were under the influence.
Driving has been defined to be as little as sleeping one off in a parking lot in the dead of winter with the engine turned over so heat gets in the car and you don't freeze to death. Under the influence can be different amounts of alcohol, marijuana, cocaine, heroin, etc.
If you have never been arrest before and you have a valid drivers license, insurance and registration, you may be eligible for ARD (Accelerate Rehabilitative Disposition). ARD means you won't have a criminal record. You may be able to ARD even if it is your second DUI or second arrest.
If you can't get ARD and it is your second DUI in Philadelphia County, you may be eligible for Philadelphia's DUI Treatment Court, which for some folks is a GREAT program.
If you can't do either of the above and you are found guilty or plea guilty, the mandatory minimum sentences depend on how many DUI's you have had in the last 10 years, the level of chemicals in your body (the BAC for alcohol), whether you cooperated during the chemical testing and whether there was an accident.
Best advice: don't drink and drive. Happy New Year!