Habitability is the characteristic of source code that enables programmers coming to the code later in its life to understand its construction and intentions and to change it comfortably and confidently... Software needs to be habitable because it always has to change...Programs are written and maintained, bugs are fixed, features are added, performance is tuned, and a whole variety of changes are made both by the original and new programming team members... What is important is that it be easy for programmers to come up to speed with the code, to be able to navigate through it effectively, to be able to understand what changes to make, and to be able to make them safely and correctly.
- R. Gabriel - Patterns of Software, Oxford Press 1996