This is the 4040th most frequent Russian word.
матеуш
The word "матеуш" does not appear to have meaning in Russian; it might be a name or a misspelling.
Here, 'Матeуш' is used as a proper noun, indicating the name of an individual.
Матeуш учится в новом университете.
Mateusz is studying at a new university.
In this sentence, 'Матeуш' is in its accusative case form (Матeуша) as it's the direct object of the verb 'встретили'.
Мы встретили Матeуша на конференции.
We met Mateusz at the conference.
Here, 'Матeуш' is used in its nominative case as the subject of the sentence.