A real-time operating system (RTOS) is a special-purpose operating system used in computers that has strict time constraints for any job to be performed and is intended to serve real time applications that possess data as it comes in , typically without buffer delays.
Types of RTOS:
Hard RTOS Firm RTOS Soft RTOS
For more details read this Article:- https://www.geeksforgeeks.org/real-time-operating-system-rtos/