Responsiveness

n. quality of being quick to respond, reactiveness

Responsiveness is a principle from interaction design / HCI, saying that a system's response to user input should happen with no perceivable delay. Responsiveness is considered a vital requirement for any user interface, and the lack of it will usually result in frustration.Other operations that take longer time should be kept in the background, giving highest priority to the user-relevant operations, such as typing, or onscreen buttons.If letting the user wait is inevitable, the system must at least show a progress bar to indicate it's busy, or something to make sure the user's command has been received and understood.
See more at Wikipedia.org...

Responsiveness Medtalk The ability to respond to a stimulus. See Airway responsiveness. [more]Responsiveness - Community and Resources

Noun
1. responsive to stimulation
(synonym) reactivity
(hypernym) sensitivity, sensitiveness, sensibility
(hyponym) excitability, irritability
2. the quality of being responsive; reacting quickly; as a quality of people, it involves responding with emotion to people and events
(antonym) unresponsiveness
(hypernym) quality

Ability of an entity to provide service within the required time. Note: The term timeliness is sometimes used incorrectly to mean responsiveness. [NATO]