What does the coach means when asked how many reps have you completed?

In a given set with too heavy weight, I assume it means how many reps have I completed to failure OR loss of form, whichever comes first ?

Sounds like you may have given the Coach negative feedback on an assigned session. In such a case, if you told the Coach that the weight was too much, you’ll get asked this. It’s referring to the point of failure, so essentially, the point at which you could not do any more work after x number of reps.