1. A localized break in a filter cake or precoat that permits fluid to pass through without being filtered. Also known as breakpoint.

2. In an ion-exchange system, the first appearance of unadsorbed ions of the type which deplete the activity of the resin bed; this indicates that the bed must be regenerated.

An interruption in the intended character stroke in optical character recognition.

A passage cut through the pillar to allow the ventilating current to pass from one room to another; larger than a doghole. Also known as room crosscut.