A fundamental characteristic of services referring to the fact that for most services the production and consumption of the service occur at the same time.

whether two events occur at the same time, said by special relativity to depend upon the observational reference frame

(Machine Safety) Concurrent events, actions, or actuations occuring within a specific time frame. This time frame is 0.5 second in a Two-Hand Control or Two-Hand Trip applications per ANSI B11.19, ANSI/RIA R15.06 and ISO 13851 (Note: ISO 13851 defines this as synchronous actuation).

The quality or state of being simultaneous; simultaneousness.

happening or existing or done at the same time

the quality of having two or more things happening at once