(Homonym: tear [crying]).
1. One of a set of rows placed one above or behind the other.
2. One of two or more layers one atop another.
3. One that ties.

A tier usually means physical separation at the machine level or, at a minimum, at the process level. A typical three-tier application architecture has the presentation layer code running on a client machine, the business logic and data access layers running on a middle-tier application server, and the database running on its own server as the third tier.

1. To place or arrange in tiers
2. To rise in tiers