This is the 97th most frequent Ukrainian word.
ці
"These."
In this sentence, 'ці' is used as a demonstrative pronoun to refer to books that are being specifically identified or discussed.
Ці книги дуже цікаві.
These books are very interesting.
Here, 'ці' modifies 'люди' to refer to a specific group of people.
Ці люди тут працюють щодня.
These people work here every day.
'Ці' is used here to indicate the specific flowers that the speaker is talking about, seen at the market.