This is the 659th most frequent Czech word.
václav
"Václav" is a Czech male given name, equivalent to "Wenceslaus" in English.
In this sentence, 'Václav' is used as a proper noun representing a person's name.
Václav jde do školy.
Václav is going to school.
Here, 'Václav' refers to the name of a Saint, Saint Václav (Saint Wenceslas).
Na svatého Václava slavíme státní svátek.
On Saint Václav's Day, we celebrate a public holiday.
The word 'Václav' is part of a proper noun referring to Saint Václav and the square is named after him.