This is the 9294th most frequent Russian word.
стас
"Стас" is a shortened form of the male name "Станислав" in Russian, used as a nickname.
In this context, 'Стас' is used as the proper name of a person, Stas, indicating a direct subject in the sentence.
Стас любит гулять по парку каждое утро.
Stas loves to walk in the park every morning.
Here, 'Стаса' is used to refer to the name Stas in the accusative case, as the object of the verb 'позвала' (invited).
Я позвала Стаса к нам в гости.
I invited Stas to visit us.
In this example, 'Стасу' represents the name Stas in the dative case, as the indirect object in the sentence.