What is the black piece called that connects the radiator hose that goes into the block and holds the hose in place?

The black piece that connects the radiator hose to the engine block and secures the hose is typically called a "hose connector" or "hose fitting." In some cases, it may also be referred to as a "thermostat housing" if it incorporates a thermostat. This component ensures a tight seal to prevent leaks and maintains proper coolant flow within the engine cooling system.