means The degree to which a material or membrane allows fluids, gases, or other substances to pass through it.

from From Latin "permeare," to pass through, built from "per-" (through) plus "meare" (to go, to pass) — the same "meare" that gives us "permeate." The abstract "-ability" suffix turned the act of passing through into a measurable property, a move that suited the language of physics and chemistry as those fields grew hungry for words describing how readily one thing moves through another.