Software consists of statements, which instruct a computer to perform the required task. A computer has no intelligence of its own and must be supplied with instructins that tell it what to do and how and when to do it. These intructions are called software.
Each part of the computer system is connected via an interface. The system can do nothing here without operating system software. Without software, a computer is a useless lump of metal.
The term software was first used in this sense by John W. Tukey in 1957; colloquially, the term is often used to mean application software. In computer science and software engineering, computer software is all information processed by computer system, programs and data.
Computer software is often contrasted with computer hardware, which is the physical substrate on which software exists. It is intrasible and has no physical existance.