An Architectural Decision (AD) is a justified design choice that addresses a functional or non-functional requirement that is architecturally significant. An Architecturally Significant Requirement (ASR) is a requirement that has a measurable effect on the architecture and quality of a software and/or hardware system. An Architectural Decision Record (ADR) captures a single AD and its rationale; the collection of ADRs created and maintained in a project constitute its decision log. All these are within the topic of Architectural Knowledge Management (AKM), but ADR usage can be extended to design and other decisions (“any decision record”).