The term 'EARLY COMPUTER OPERATING SYSTEM' can be summarized by the four-letter word UNIX. UNIX is a computer operating system that was developed in the late 1960s AT AT&T Bell Labs by Ken Thompson, Dennis Ritchie, and others. It is one of the earliest operating systems and is still widely used today. UNIX is known for its stability, scalability, and portability, making it a popular choice for many applications.