Bed (geology)

In geology a bed is the smallest division of rock or deposit. It is a geologic formation or stratigraphic rock series marked by well-defined divisional planes (bedding planes) separating it from layers above and below. 
A bed is the smallest lithostratigraphic unit. It ranges in thickness from a centimetre to several metres. It can be distinguished from beds above and below it by rock or mineral type and particle size. The term is usually applied to sedimentary strata, but may also be used for volcanic flows or ash layers.
In a quarry, bedding is a term used for a structure occurring in granite and similar rocks which allows them to split in well-defined planes horizontally or parallel to the land surface.
Engineering.
In geotechnical engineering a bedding plane often forms a discontinuity that may have a large influence on the mechanical behaviour (strength, deformation) of soil and rock masses. This is important in, for example, tunnel, foundation, or slope construction.