simultaneous

As an adjective simultaneous

is occurring or transpiring at the same time.

As a noun coöccurrence is

the fact of a thing occurring simultaneously with something else; correlation.

As an adjective simultaneous

is occurring]] or [[transpire|transpiring at the same time.

As a noun simultaneum is

a simultaneous occurrence of unrelated events.

As adjectives the difference between simultaneous and multiuser

is that simultaneous is occurring]] or [[transpire|transpiring at the same time while multiuser is (computing|telecommunications) having capabilities for serving many users simultaneously.