(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. See application server and client/server.
Middle-tier Sentence Examples
In the Abietineae the cells of the middle tier elongate and push the lowest tier deeper into the endosperm; the cells of the bottom tier may remain in lateral contact and produce together one embryo, or they may separate (Pinus, Juniperus, &c.) and form four potential embryos.
The middle tier is divided by a diagonal heather ledge, running from bottom left to top right.
The middle tier of the system is the Application Server Layer.
When cutting the wedding cake, the couple will simply cut a middle tier and the false layers will not be noticed.