This is the 678th most frequent Polish word.
stanisław
"Stanisław" is a Polish male given name, meaning "someone who achieves glory" or "famous for being steadfast."
In this sentence, 'Stanisław' is used as a proper noun, specifically a common given name.
Stanisław to popularne imię w Polsce.
Stanisław is a popular name in Poland.
Here, 'Stanisława' is the accusative form of the proper noun 'Stanisław,' indicating the direct object of the verb.
Poznałem Stanisława wczoraj na spotkaniu.
I met Stanisław yesterday at the meeting.
In this instance, 'Stanisławie' is the locative form of the proper noun 'Stanisław,' following the preposition 'o' which requires the locative case.