This YouTube video, titled "Class 5 | Pre action sprinkler system," is part of a series that explains different types of sprinkler systems. The video focuses on pre-action systems, which are similar to dry pipe systems but use a supplemental detection system to trigger water release. The video explains that pre-action systems are often used in sensitive environments, like computer rooms or museums, to protect against water damage while still providing protection against fire. The video then details three different types of reaction systems: single interlock, non-interlock, and double interlock, explaining their specific applications and limitations.