Crowd counting
Crowd counting

Crowd counting - Wikipedia

Crowd counting is the act of counting the total crowd present in a certain area. The people in a certain area are called a crowd. The most direct method is to actually count each person in the crowd.
Since the early 2000s, there has been a shift in the understanding of the phrase “crowd counting”. Having moved from a simpler crowd counting method to that of clusters and density maps, there are several improvements for crowd counting methods. Crowd counting can also be defined as estimating the number of people present in a single picture.
The only correct method is to count everyone upon entry. Everything else is an estimate.
according to the article that's the "modern understanding"
Still the sole correct method. An estimate isn't the same as counting.