incompresible

The term "incompresible" is not standard; it is commonly a misspelling of "incompressible." In physics and mathematics, incompressible describes systems whose density or volume is preserved under pressure or deformation.

In fluids, incompressible fluids have density that remains nearly constant under pressure changes; liquids are treated as incompressible in many analyses because their bulk modulus is large. Incompressible flow is modeled by the Navier–Stokes equations with the divergence-free condition, ∇·v = 0, and is valid when the Mach number is small (typically much less than 1).

In materials science, compressibility measures how volume changes with pressure; a small compressibility means near-incompressible behavior.

In mathematics, incompressibility has related concepts: incompressible flows preserve volume (Liouville's theorem) and, in topology, an incompressible surface cannot be compressed into a simpler surface within a manifold.

Etymology: from Latin incompressibilis; the prefix "in-" meaning not, "compress-" to press together, "-ibilis" able. Spelling note: the standard English adjective is "incompressible." When you encounter "incompresible," treat as a misspelling.