This is the 4153rd most frequent Polish word.
byliście
"You (plural) were."
The word 'byliście' refers to the plural, second person past tense of 'to be', indicating that 'you all' were present in some location or state.
Byliście na wakacjach w górach.
You were on vacation in the mountains.
Here, 'byliście' continues to convey the plural, second person past tense 'you all', asking about their state of satisfaction after watching a movie.
Czy byliście zadowoleni z filmu?
Were you satisfied with the movie?
In this example, 'byliście' identifies the past condition of 'you all', expressing a state of being unprepared for an event.