> [Self-plagiarism] doesn't mean "I use the same turn of phrase every once in a while". It means "I reproduced substantial portions of prior research or other text of my own and passed it off as new research."
The term is not used to mean occasional repetition of phrases or concepts, nor does it apply when that expectation is not the production of new research (e.g. when delivering a course lecture). The term is used to mean something more along the lines of when you take a paper you published some time ago, make a few edits, and re-submit it to another journal.
I once reviewed a paper. It seemed familiar. I pulled up a paper by the same authors from a decade previous. Yup, the first 10 pages were almost identical. I had read the earlier paper, and others had cited it -- though not the authors.
That was a waste of time, adding nothing to the dialog.