This is the 511th most frequent Polish word.
jednocześnie
"At the same time" or "simultaneously."
Here, 'jednocześnie' is used to express that two actions are occurring at the same time.
On pisał na komputerze i jednocześnie rozmawiał przez telefon.
He was typing on the computer and simultaneously talking on the phone.
'Jednocześnie' is applied to link two characteristics occurring together during the meeting.
To spotkanie było ciekawe i jednocześnie bardzo produktywne.
This meeting was interesting and at the same time very productive.
In this sentence, 'jednocześnie' conveys the simultaneous necessity of two actions.