A stock phrase phrase
A phrase that has been used so often that is often considered uninteresting or deemed as a sign of bad writing.
Since the teacher will give higher marks to creative students, you should avoid using this stock phrase.
I didn't even bother reading his essay when I saw the stock phrase "In a nutshell".
If the examiner sees some stock phrases in your writing, you will lose points in the criteria called "task response and lexical resource."
The origin of this phrase is not clear.