It's not so long ago that, when glancing through job adverts, the term n-tier architecture would crop up as something that potential candidates needed to be familiar with. The principle behind this architectural paradigm was that there was a data store that was typically held on a company-owned server; then, there was a service (or several services) that would interrogate that data at the behest of either the client application, or of another service, and you would have a client application (be that a desktop or web client) that communicated with the service. The architecture is typically illustrated as follows:
The term n-tier overtook three tier as the service in that diagram could actually call another service and so there could, feasibly, be several layers between the client and...