This is the 470th most frequent Russian word.
чаще
More often.
Here, 'чаще всего' is a set phrase meaning 'most often' or 'as a rule', used to describe the usual occurrence of an action.
Чаще всего я читаю перед сном.
Most often, I read before sleeping.
The word 'чаще' is used as a comparative adverb meaning 'more often', indicating an increased frequency of an activity.
Я стал бегать по утрам чаще.
I started running in the mornings more often.
In this example, 'чаще' again means 'more often' and compares current frequency with a previous one.