The word program is used in two ways: to describe individual instructions, or source code, created by the programmer, and to describe an entire piece of executable software. This distinction can cause enormous confusion, so we will try to distinguish between the source code on one hand, and the executable on the other.

New Term: A program can be defined as either a set of written instructions created by a programmer or an executable piece of software.

Source code can be turned into an executable program in two ways: Interpreters translate the source code into computer instructions, and the computer acts on those instructions immediately. Alternatively, compilers translate source code into a program, which you can run at a later time. While interpreters are easier to work with, most serious programming is done with compilers because compiled code runs much faster. C++ is a compiled language.