compressions

Compressions is the plural of compression, and in common usage refers to processes that reduce the size or volume of something or to the act of applying pressure. The term appears in several domains with related but distinct meanings: medicine, information technology, acoustics, and physics.

In medicine, chest compressions refer to the manual or automated compression of the chest to maintain circulation during cardiac arrest. Effective chest compressions help propagate blood to vital organs until normal heart function is restored, and they are typically performed in cycles in combination with rescue breaths or as continuous compressions depending on the protocol.

In information technology, compression reduces the size of data for storage or transmission. Lossless compression preserves all original information (for example ZIP archives, PNG images, FLAC audio), while lossy compression discards some data for higher reduction (such as JPEG images, MP3 audio). Techniques include entropy coding, dictionary methods like LZ77, and transform-based coding.

In acoustics and audio engineering, compression refers to dynamic range compression, a process that reduces the difference between loud and soft sounds. A compressor adjusts signal levels according to parameters such as threshold, ratio, attack, and release to achieve a more consistent sound.

In physics and engineering, compression describes the reduction in volume of a material when subjected to external pressure. Materials are characterized by properties such as compressibility and bulk modulus, and the ability of structures to withstand compressive forces is described by their compressive strength.