Hepatitis is a general term for infections by any of a large family of related viruses which, in humans, cause several diseases. One or two are gastroenterological diseases, spread in contaminated food, and usually term limited in most of those infected. Others are longer term infections, several of which cause, among other things, inflammation of the liver. The clinical signs and prognosis, as well as the therapy, vary with the virus. A few of them are serious infectins and even lead to death in some of those infected.
Several varities can be transfered between sexual partners, certainly by what are termed unsafe sexual practices. However, the mode of transmission of several varieties is not well known. There are vaccines for one or two of the viruses in the family, and only symptomatic treatement for the rest.
For a detailed description of the virus family, and their various medical implications, see the Wikipedia article on hepatitis.