General

Pressure developed in opposition to the flow of liquid or gas in a pipe, duct, conduit, etc.; due to friction,

The placing of timbers, usually set in a diagonal or oblique position, to hold a wall in place.

The flowing back of used, contaminated, or polluted water from a plumbing fixture or vessel into the pipe which feeds

The leaf in a window shutter that folds behind the exposed leaf of the shutter; that part of a window shutter that folds