Definition 0.1. A program (or computer program/software) consists of an ordered set of logical instructions that are processed or executed by the computer hardware; this is carried out either sequentially (by one processor) or in parallel (as in parallel computation or multitasking by several processors operating in parallel). The computare hardware that executes the program usually consists of either one or several computer central processing units (CPUs), often also controlling peripherals, such as computer monitor(s), printers, scanners, digital cameras, speakers, etc.

Mathematically, any computer program can be expressed in terms of recursive functions and/or algorithms. Computer programs are “executable programs or the source code from which executable programs are derived (e.g., compiled)”. Often the distinction is made between the basic machine language and higher-level languages/programming languages that are then translated (or compiled) into the machine language.