A site specific constant is often called a "Pepper" as an aside. Just helps people google it if they want more information.
Several implementations utilise a Salt + Papper (unique per user value and single per site value). A Pepper is particularly useful when it is NOT stored in the database (e.g. stored in an environmental variable or even code). That way if someone steals your database via SQL Injection or a database backup file, they'd have to break the Pepper to recover passwords.
Peppers only make sense when they're almost "free" to implement. A slow hashing scheme is the most important thing, then unique salting, and finally a pepper last (since a pepper adds the least security wise).
Several implementations utilise a Salt + Papper (unique per user value and single per site value). A Pepper is particularly useful when it is NOT stored in the database (e.g. stored in an environmental variable or even code). That way if someone steals your database via SQL Injection or a database backup file, they'd have to break the Pepper to recover passwords.
Peppers only make sense when they're almost "free" to implement. A slow hashing scheme is the most important thing, then unique salting, and finally a pepper last (since a pepper adds the least security wise).