This is the 442nd most frequent Hungarian word.
egyszerre
"At the same time" or "simultaneously."
Here, 'egyszerre' is used to mean 'at a time', suggesting a limit of performing one action during a single moment.
Egyszerre csak egy dolgot csinálj.
Only do one thing at a time.
In this context, 'egyszerre' is used to mean 'simultaneously', indicating the audience clapped together at the same time.
A színdarab végén a közönség egyszerre tapsolt.
At the end of the play, the audience applauded simultaneously.
Here, 'egyszerre' means 'at the same time', implying that all the guests arrived together at one moment.