Examples of grey charges are automatic renewals, mischarges, and uncorrected billing errors. It's money that isn't illegally charged, but most consumers don't realize that they are paying money that they never planned on paying.
One of the things that has gotten us a few times is the "free trial" that automatically converts to a full charge after a certain number of days, unless you cancel. It's important for consumers to look over their bills. Make sure they are right and fix any errors as soon as you see them. Another one that has gotten us in the past was shipping and handling charges, sometimes they are higher than the actual product purchased.
Be a careful consumer and check your bills monthly. Especially during this busy shopping season, don't let dollars trickle out of your budget.