This is the 369th most frequent Korean word.
만
"만" means "only" or "just."
Here, '만' is a particle indicating exclusivity, meaning 'only' in this context.
나는 커피만 마셔요.
I only drink coffee.
In this sentence, '만' is used to express that the activity of walking was the sole action performed.
오늘은 산책만 했어요.
Today, I only went for a walk.
Here, '만' highlights that the action applies exclusively to 'that person' and no one else.