This is the 4113th most frequent Japanese word.
マーク
"Mark" (symbol, sign, or indication).
Here, 'マーク' refers to an indicator or sign used to denote something, such as marking an answer in a test or annotation.
彼はこの問題にマークをつけた。
He marked this issue.
In this context, 'マーク' is used to describe a literal mark or symbol observed on a surface.
道路に青いマークがありました。
There was a blue mark on the road.
Here, 'マーク' is utilized in a sports context where it means to guard or keep track of an opposing player actively.