means The quality of consistently performing as expected, so that people can depend on you or something to deliver every time.

from From 'rely' plus '-ability.' 'Rely' came into English in the late medieval period from Old French 'relier,' to bind together or fasten, which traces back to Latin 'religare' — 're-' (back) plus 'ligare' (to bind), the same root that ties up 'ligament' and possibly 'religion.' So buried in the word is a literal image of binding fast: when you rely on something, you're tying yourself to it. The abstract noun 'reliability' is a much later formation, an 18th- or 19th-century coinage that bolted the '-ability' suffix on to make dependability measurable.