komprimierbar

Komprimierbar is a German adjective meaning capable of being compressed; it is derived from komprimieren, to compress. In everyday language it describes a substance, object, or data that can be reduced in volume, length, or size under external pressure or encoding.

In physics, komprimierbarkeit refers to the extent to which a material’s volume changes when pressure is applied. The standard measures are the isothermal compressibility κ_T = - (1/V) (∂V/∂P)_T and the adiabatic compressibility κ_S = - (1/V) (∂V/∂P)_S. The reciprocal of κ_T is the bulk modulus K; κ_S relates to the speed of sound. For gases, κ_T is relatively large (for an ideal gas at pressure P, κ_T = 1/P), while liquids and especially solids are much less komprimierbar; typical bulk moduli range from around 2 GPa for water to hundreds of GPa for most metals. In high-speed aerodynamics or acoustics, compressibility effects become important beyond low Mach numbers.

In information technology, komprimierbar also describes data or files that can be represented with fewer bits than their original form. Data compression relies on redundancy or irrelevancies; methods may be lossless (e.g., Huffman, LZ77) or lossy. A file is komprimierbar if a lossless encoding can reduce its size; some data (e.g., highly random or encrypted) may be effectively incompressible.