What does it mean for a fire to be X % contained?

Question

What does it mean for a fire to be X % contained?

Answer 1

x is used to represent a place where any number between 0 and 100 can be placed.

Making it: the fire is 20% contained or 80% contained.

containing a fire is exactly that... controlling the fire around its perimeter. If the fire is controlled around 80% of its perimeter, then it is 80% contained.