This is the 103rd most frequent Polish word.
ludzi
The word "ludzi" in Polish means "people" (genitive case).
Here, 'ludzi' is used as the genitive plural form, referring to people in context of a larger group.
Wiele ludzi przyszło na koncert.
Many people came to the concert.
In this sentence, 'ludzi' is the plural genitive form, used after the noun 'grupa' that dictates genitive.
Widziałem grupę ludzi spacerujących po parku.
I saw a group of people walking in the park.
Here, 'ludzi' indicates people in an abstract, qualitative sense and is in the genitive plural due to 'więcej'.