This is the 8878th most frequent Polish word.
saudyjczyków
"Saudyjczyków" means "of Saudis" or "Saudi people" (genitive plural form in Polish).
In this sentence, 'saudyjczyków' is used in the plural accusative form to refer to Saudi people as the object of the verb 'mieszka' (live).
Wielu saudyjczyków mieszka w Rijadzie.
Many Saudis live in Riyadh.
Here, 'saudyjczyków' is in the plural instrumental form, used to indicate individuals of Saudi nationality as the instrument in the context of interaction during the conference.
Rozmawiałem z grupą saudyjczyków podczas konferencji.
I spoke with a group of Saudis during the conference.
In this case, 'saudyjczyków' is in the possessive genitive plural form, used to indicate possession or association, referring to the history belonging to or associated with the Saudi people.