On-demand definition: An on-demand service is available at any time that you want to use it. Demand definition is - an act of demanding or asking especially with authority. Cable television is being replaced in many homes by on-demand video services. See more. Learn more. See also: demand, on on demand When needed or asked for, as in She's always ready to sing on demand, or Nowadays infants are generally fed on demand. on demand definition: 1. at any time that someone wants or needs something: 2. available when a customer wants or asks…. It can be difficult to adjust to a baby's need to feed on demand. Often hyphenated. on demand When needed or desired. How to use demand in a sentence. Synonym Discussion of demand. | Meaning, pronunciation, translations and examples On demand definition, to ask for with proper authority; claim as a right: He demanded payment of the debt.