A computer consists of a collection of process they are classified as two categories:

1. Operating system process which is executed by system code.

2. User processes which is executed by user code.

A process means program in execution. It generally takes an input, processes it and gives us the appropriate output. Check Introduction to Process Management for more details about a process. There are basically 2 types of processes.

1. Foreground processes: Such kind of processes are also known as interactive processes. These are the processes which are to be executed or initiated by the user or the programmer, they can not be initialized by system services. Such processes take input from the user and return the output. While these processes are running we can not directly initiate a new process from the same terminal.
2. Background processes: Such kind of processes are also known as non interactive processes. These are the processes that are to be executed or initiated by the system itself or by users, though they can even be managed by users. These processes have a unique PID or process if assigned to them and we can initiate other processes within the same terminal from which they are initiated.