'On demand' definitions:

Definition of 'On demand'

From: GCIDE

Demand \De*mand"\, n. [F. demande, fr. demander. See Demand, v. t.]
1. The act of demanding; an asking with authority; a peremptory urging of a claim; a claiming or challenging as due; requisition; as, the demand of a creditor; a note payable on demand. [1913 Webster]
The demand [is] by the word of the holy ones. --Dan. iv. 17. [1913 Webster]
He that has confidence to turn his wishes into demands will be but a little way from thinking he ought to obtain them. --Locke. [1913 Webster]
2. Earnest inquiry; question; query. --Shak. [1913 Webster]
3. A diligent seeking or search; manifested want; desire to possess; request; as, a demand for certain goods; a person's company is in great demand. [1913 Webster]
In 1678 came forth a second edition [Pilgrim's Progress] with additions; and then the demand became immense. --Macaulay. [1913 Webster]
4. That which one demands or has a right to demand; thing claimed as due; claim; as, demands on an estate. [1913 Webster]
5. (Law) (a) The asking or seeking for what is due or claimed as due. (b) The right or title in virtue of which anything may be claimed; as, to hold a demand against a person. (c) A thing or amount claimed to be due. [1913 Webster]
In demand, in request; being much sought after.
On demand, upon presentation and request of payment. [1913 Webster]