What was the term "Monitor" used to describe in the context of early operating systems?

In the early days of computing, the term "Monitor" referred to a type of operating system that managed and controlled the execution of programs on a computer system. These early monitors were responsible for managing the execution of jobs, handling input and output operations, and providing basic control over the hardware resources of the system. They were fundamental in enabling multitasking and job scheduling, allowing the computer to handle multiple tasks and users efficiently. Early operating systems, such as those used in mainframes and early computers, were often called "Monitors" because they "monitored" and controlled the system's operations, ensuring that programs ran smoothly and system resources were allocated effectively.