In built-up roofing, a weather-resistant (flexible or semiflexible) covering consisting of alternate layers of felt and bitumen, fabricated in a continuous covering and surfaced with aggregate or asphaltic material.

1. The medium through which the fluid stream is passed for purposes of filtration.

2. The ion-exchange medium used in dialysis, diffusion, osmosis and reverse osmosis, and electrophoresis.

A thin layer of tissue surrounding a part of the body, separating adjacent cavities, lining cavities, or connecting adjacent structures.