Final answer:
A tertiary square is a small square within a secondary square in a hemocytometer. They are used to accurately count cells and calculate cell concentration.
Step-by-step explanation:
In a hemocytometer, a tertiary square is a small square within a secondary square. A hemocytometer is used to count cells in a given sample. The number of tertiary squares in a secondary square can vary depending on the specific design of the hemocytometer. These squares are used to accurately count the cells and calculate cell concentration.