Final answer:
The right that ceases to exist if enforcement of a building restriction is not pursued within a certain period of time is known as liberative prescription. This concept is like a statute of limitations that applies to civil matters, preventing legal action after the designated time has lapsed.
Step-by-step explanation:
If a noticeable violation of a building restriction occurs and nobody stops it, after a certain period of time the right to stop the violator no longer exists. This right is known as liberative prescription, which means that as time passes without action being taken, legal enforcement may no longer be possible due to the passage of time. The concept is similar to the statute of limitations in criminal law, where if legal action is not commenced within a specific time frame, the right to prosecute expires.