Heuristic

A heuristic is an informal rule-of-thumb is software design.

Software design draws on heuristics constantly, from object-oriented design guidelines such as "favor composition over inheritance" to user-interface heuristics such as Jakob Nielsen’s usability guidelines.

Unlike a design principle, which is usually justified by an underlying rationale about why it tends to hold, a heuristic’s value lies in narrowing the space of options quickly, rather than settling a design question conclusively.