Definition of instance

An object in relation to the class to which it belongs. For example, an object myList that belongs to a class List is an instance of the class List.

A copy of a master, which you create by dragging the master from a stencil to a drawing.

A unique occurrence of a runbook that is running on a runbook server.

A unique occurrence of an application, such as Microsoft Dynamics CRM or Netbreeze, for online customers.