What is Hell?:
The word hell comes from a Germanic root which means to cover, and is the usual translation of the Hebrew Sheol. In religions in the West, hell is believed to be a place of punishment for the souls of those who sinned during their lives. Hell is normally contrasted with heaven, the place where the souls of good people go to be rewarded.
What is Sheol?:
The word sheol is a Hebrew word for grave or pit. Theologically, it was an underworld where the sprits of the dead lived on. It was similar to the Greek Underworld and was thus not normally a place of punishment. Some later texts, however, started to refer to Sheol in a negative manner, as if it were reserved for those who did evil while alive.
What is Limbo?:
Limbo is not quite hell and not quite heaven. The term limbo comes from the Latin word limbus, which means border or edge. In Roman Catholic doctrine, limbo is the immediate destination of those souls who, through no personal fault, are not admitted to heaven. Because this fate is not due to their own moral failings, they are also not damned to hell. The name limbo comes from the fact that it is traditionally believed to be located on the edge of Hell.
God & Hell:
The existence of hell is theologically necessary in Christianity because of the need to punish those who refuse to believe correctly. It is also a theological problem because it has come to be seen as a place of eternal torment. It is doubtful that this is compatible with the existence of a God which is perfectly loving.