What does forestry Class day………., mean?

WHAT DOES THE CLASS DAY MEAN?
Class 1: Low
Fires are not likely.
Class 2: Moderate
Fires are possible in light fuels.
Class 3: High
Fuels in open areas and sunny slopes may spread rapidly
Class 4: Very High
Fires spread and increase in intensity rapidly
Class 5: Extreme
Fires will spread very rapidly.