What is it meant by optimum temperature? In other words, how is the enzyme functioning below and above optimum temperature?

Optimum temperature in enzymes mean, the maximum temperature that an enzyme is most active in.

Explanation:

Temperature affects enzymes and their functioning. Optimum temperature refers to temperature in which an enzyme best functions in. This is where it is at its best catalytic state.

High temperatures above 50°C denatures protein (enzymes) by interfering with their structures whereas low temperatures renders them inactive. They stay in a dormant state that gets activated when they are shifted to their optimal temperature range (30°C to 50°C)