This is the 200th most frequent Czech word.
petra
"Petra" is a proper noun, commonly used as a female given name in Czech, equivalent to "Petra" in English.
Petra is used as a proper noun here, referring to a person's name.
Viděla jsem Petru v parku.
I saw Petra in the park.
Petra is used here in plural form to refer to specific items, illustrating a rare usage of the term.
Vyřezávali petry ze dřeva.
They were carving petros from wood.
Petra is used as a noun here, referring to a meaning of the word in a different language.