This is the 834th most frequent German word.
manche
"Manche" in English means "some" or "a few".
In this sentence, 'manche' acts as a pronoun referring to an indefinite quantity of people.
Manche Menschen lieben es, früh aufzustehen.
Some people love getting up early.
Here, 'manche' functions as a determiner modifying the noun 'Bücher', indicating an unspecified subset.
Ich habe manche Bücher schon gelesen, aber nicht alle.
I have already read some books, but not all.
In this example, 'manche' is used as a noun substitute representing an unspecified group of people.