In my understanding, a key holder is commonly known as key chain or key purse. It will help you organize your keys and very convenient to carry. While key rack is where you keep your keys including your key chain. It can be shelf, stand frame or box. We usually find it in a house.:lol:
I am not a teacher, any corrections with my grammar construction are welcome. Thanks.
:?: That definition of "key holder" sounds like our (Br English) "key ring". In British English a "key holder" is usually (? - always, in my experience) a person. If a shop's burglar alarm rings in the middle of the night, the police contact the key holder.