Strictly or rigidly adhered to; strong, binding, and clearly defined. Used especially to describe rules. I have some hard and fast rules in my company; break them, and you're out of here.The duties you're responsible for are hard and fast, so don't become lax in your role.
Defined, fixed, invariable, as in We have hard and fast rules for this procedure. This term originally was applied to a vessel that has come out of water, either by running aground or being put in dry dock, and is therefore unable to move. By the mid-1800s it was being used figuratively.