What does 'extra sharp, sharp, medium and mild' Cheddar cheese all mean?

When cheese is made its allowed to sit and mold for certain periods of time in whats known as a brine, This is acidic giving the cheese its sharpness, the longer it sits the Sharper it is. often the brine is made from Salt, ginger and roots of other various plants in boiled water, The cheese is often washed with this for months before it is released into the market