Answer : 1. "Operating system"
Explanation :

1. The operating system runs on computer hardware and provides the platform to run other software.

2. The computer takes the help of various devices and programs to do its work. There is a separate and special computer program to handle these devices and programs, this special master program is known as the operating system.

3. Operating System, in short form is called OS, is a computer program which operates other computer programs. The operating system acts as an intermediary between users and the computer system. It explains our instructions to the computer. Other software programs and hardware are operated through the operating system.