Not really sure this requires a definition. It seems pretty obvious. Unfortunately, I see this as a problem, and wonder what would be an effective solution.

I've seen some gate agents, "publicly shame" passengers by loudly announcing that the offending passenger is boarding group X, as their boarding pass clearly states, and is not boarding as everyone else around them is boarding group X-1, which is the group that is boarding per the announcement made and also pointing to the large monitor behind the counter that clearly states boarding group X-1 is now boarding, and then reject their boarding, and telling them to wait until their boarding group has been called.

I figure that must be effective to curb behavior over time, but not all gate agents seem to enforce/utilize this policy, which makes it ineffective.

If this is to improve, I'm guessing it has to be a form of public shaming/humiliation/embarrassment and/or a penalty/fine/consequence.