This lecture introduces the final modifier in Java, which is used to indicate program elements that should not be modified/redefined/extended. It covers the usage of final for classes, methods, attributes, and variables, highlighting its importance and restrictions. Examples include final methods preventing subclass overriding and final classes prohibiting subclass extension. The lecture also discusses the implications of having final variables and references to objects, emphasizing the immutability aspect. Overall, the final modifier ensures the integrity and stability of Java programs.