This is the 770th most frequent Polish word.
wielu
"Many" or "of many" (dependent on context).
Here, 'wielu' is used as an indefinite quantifier to express 'many' in relation to the noun 'ludzi' (people).
Wielu ludzi lubi wieczorne przedstawienia.
Many people enjoy evening performances.
In this sentence, 'wielu' modifies the noun 'okazji' (opportunities), again serving as a quantifier meaning 'many.'
Nie miałem wielu okazji, aby porozmawiać z nią.
I haven't had many opportunities to talk to her.
'Wielu' here emphasizes the quantity of 'uczestników' (participants) while indicating a subset of a group.