What is a process?
A process is simply a program in execution: an instance of a program execution.
Unit of work individually schedulable by an operating system.
OS keeps track of all the active processes and allocates system resources to them according to policies devised to meet design performance objectives.
To meet process requirements OS must maintain many data structures efficiently.
The process abstraction is a fundamental OS means for management of concurrent program execution. Example: instances of process co-existing.