Licences come in three flavours
Single-user licences allow the software to be installed on a single computer.
Multi-user licences are the same as single user, but the price is discounted to reflect volume purchased. The software can be installed on the number of computers that a licence is purchased for.
Multi-user licences must be used by the organisation that purchases them - they can't be split. For example if Bloggs Corp purchases a 5-user licence, then they are entitled to install the software on 5 computers that are used by Bloggs Corp in their normal course of business. Requests for variations will be considered on a case-by-case basis, e.g. a bulk order from a club.
Network licences allow the software to be installed on a network server (in fact, the software can only be used from a network server). The number of seats purchased is determined by counting the total number of computers connected to the local area network. The price structure of the network licence reflects the fact that only a fraction of the users on a network will be accessing the software at any one time.
The network version of the software is "zero-install" - there is no software to be installed on the client computers.