A regulatory takings, named after the Fifth Amendment to the U.S. Constitution, refers to situations where a government imposes regulations on a property that reduce the value of the property, but without actually seizing it as when the power of eminent domain is exercised.
The relevant clause in the Fifth Amendment says "nor shall private property be taken for public use without just compensation."
The ability of units of government to "take" a property's value through imposing restrictions on its use that reduce its value is specifically known as "regulatory takings" because it is done through imposing various regulations.