This is the 371st most frequent Czech word.
platí
"Platí" means "it applies," "it is valid," or "it pays."
In this sentence, 'platí' means 'is valid' or 'applies', indicating the time validity of the ticket.
Tento lístek platí jen na dnešní den.
This ticket is valid only for today.
Here, 'platí' is used in the sense of 'pays', describing the act of transferring money to settle a transaction.
Pán platí za svůj nákup v hotovosti.
The gentleman pays for his purchase in cash.
In this context, 'platí' means 'holds true' or 'is valid', introducing a general proverb or rule.