This is the 387th most frequent Polish word.
mariusz
The Polish word "Mariusz" is a masculine given name, equivalent to "Marius" in English.
Here, 'Mariusz' is used as a proper noun referring to a person, specifically indicating the speaker's friend.
Mariusz jest moim przyjacielem.
Mariusz is my friend.
'Mariusz' is again used as a proper noun, specifying the name of the individual the speaker met with.
Poszedłem na spotkanie z Mariuszem.
I went to a meeting with Mariusz.
In this case, 'Mariusz' is utilized as a direct form of address, calling the person's attention and indicating whom the question is directed at.