Single Tier Web Application

A single-tier application is an application where the user interface, backend business logic & the database all reside in the same machine.

What is meant by single-tier architecture?

A single-tier architecture is an architecture in which the entire application resides on the user's machine. Before networking became so easy and cheap, this was fre- quently the design of choice. ... The obvious drawback to single-tier architecture is that the data lives on a local machine, and no one else can access it.