Internal documentation

Computer Software is said to have Internal Documentation if the notes on how and why various parts operate is included in the source code as comments. It is often combined with meaningful Variable names with the intention that another programmer some time in the future can easily read straight through the code and gain a reasonably good understanding of what it does and how it does it.

This contrasts with external Documentation where programmers keep their notes and explanations elsewhere.

Internal documentation has become increasingly popular as it cannot be lost, and any programmer working on the code has it immediately to hand and knows that it exists.