In passing

What is In passing?

In passing definition and meaning on Dictionary terms:
adjective

going by or past; elapsing: He was feeling better with each passing day.
brief, fleeting, or fortuitous; transitory: to take a passing fancy to something.
done, given, etc., in passing; cursory: a passing mention.
surpassing, preeminent, or extreme.
indicating satisfactory performance in a course, on a paper, in a test, etc.: a passing grade on a test.