Population density is the right term.
Population density of any species (plant, animal or humans) is the number of individuals found in a given unit of area. It is usually expresses as “X” species in “Y”
X = number of species
Y = unit of area , it can be square feet, Square meter, Square kilometer, Square yard etc.
For example , population of 1000 insects living in an area fo 1000 square feet has a population density of 1000/1000 insects per square feet = 1 insect per square feet.