Answer:
The teacher is trying to say that there is a subject-verb error
Step-by-step explanation:
When checking the writing in a piece of work, there are specific symbols to put little notes where the errors happen, the abbreviation S/V is used when there is a subject-verb agreement mistake, this is when it is used the incorrect verb form with any of the persons in the speech, for example, "The day is beautiful" instead of the correct form "The day is beautiful"