Options contain all the little details of everything in your spaces. An item is a place holder for what will go into a space and the options in that item represent the possibilities that can fulfill that placeholder. A confirmed option indicates that a final choice has been made on what will be used for that item.
An option can be shared by many items/spaces. This is common with items such as flooring, paints, windows, doors, trim, etc.
Once confirmed, no other option can be confirmed for that item.
Further Reading: