This is the 113th most frequent German word.
mehrere
"Mehrere" means "several" or "multiple" in English.
Here, 'mehrere' precedes the noun 'Städte' (cities) to express that the subjects visited a number of cities, more than one but not exactly specified.
Sie besuchten mehrere Städte während ihrer Reise.
They visited several cities during their trip.
In this sentence, 'mehrere' (several) is used as an indefinite numeral to indicate an unspecified yet multiple quantity of items, modifying the noun 'Bücher' (books).
Ich habe mehrere Bücher gelesen.
I have read several books.
In this case, 'mehrere' is used to describe the noun 'Gründe' (reasons), emphasizing that the decision was based on more than one rationale or cause.