What is an instar?

Molts divide an insect’s life into stages that are known as stadia.

Between hatching from its egg and its first molt, an insect is in the first stadium and is known as the first instar.

Between the first and second molts, the second stadium, it is known as the second instar, and so on until it attains the status of adult instar, after which all but the most primitive insects do not molt.