Modules are logical service based groups of output. Modules have many configuration options that relate to the rota behaviour within them.
Rotas are logical sub-groupings of module output and usually match the preferred approach of a rota team
Sites are places where work can happen. They can also be virtual but they tell a person where they are working. Sites can be a part of more than one rota
Rooms are fixed places at sites. They have a capability and a capacity