A three-way interaction in a client/server environment, in which the user interface is stored in the client, the bulk of the business application logic is stored in one or more servers ...
(1) Generally refers to the processing that takes place in an application server that sits between the user's machine and the database server. The middle tier server performs the business logic.
"In FY18, HPE will cease selling custom-designed, commodity servers to Tier 1 Service Providers, which we define as Amazon, Google, Microsoft, Facebook, Apple, TenCent, Alibaba and Baidu.