Master Keying is a locksmith term used to describe a situation where one key fits all the locks while other keys work some of them. This would be useful where your gardener and pool guy only need access to your yard gates, while your key works the yard gates and your entire home.
Construction Keying is when copies of the “construction” key are passed out to the various contractors working a job. After the job is completed and the owner’s key is inserted into the keyway and turned, the construction keys no longer work. This saves having to have a locksmith re-key a second time. Construction Master Keys are also available for multiple projects.
Common Area Keying is almost the opposite of master keying. It’s where many different keys all work in one lock, for example; all 50 different apartment keys can open the front door of the building.
Finally there is Random Access Keying. This is where certain keys work in particular sets of locks, and is set up on a lock by lock basis, rather than the hierarchy usually found in master keying.