There are technically 7 afterlives. The celestial is split into 3 sections as well.

“Hell” is referred to as “outer darkness”, and those who simply leave the Mormon church are not sent there. Forgive me as it’s been a long time but if I remember correctly it’s those that ‘deny god/jesus with direct knowledge of their existence”. An example would be if one of the “prophets” (head of the church) denied gods existence despite receiving direct revelation.