"Informal description of a functional requirement or product property in XP. A user story serves as the basis for acceptance tests that formally check whether the product complies with the described function or property." (Johannes Link & Peter Fröhlich, "Unit Testing in Java", 2003)
"A requirement formulated into a small number of sentences in the user’s natural language. User stories are common in Extreme Programming (XP)." (Bruce P Douglass, "Real-Time Agility", 2009)
"A short narrative that explains who wants something to happen in a piece of software, what they want, and why they want it." (Jon Radoff, "Game On: Energize Your Business with Social Media Games", 2011)
"A narrative description of a software requirement, function, feature, or quality attribute presented as a narrative of desired user interactions with a software system." (Project Management Institute, "Software Extension to the PMBOK® Guide" 5th Ed., 2013)
"A short story explaining how the system will let the user do something." (Rod Stephens, "Beginning Software Engineering", 2015)
"A tool used in Agile software development to capture a description of a software feature from an end-user perspective. The user story describes the type of user, what he or she wants, and why. A user story helps to create a simplified description of a requirement." (Pierre Pureur & Murat Erder, "Continuous Architecture", 2015)
"Description of the functionality that a product should have, written from the perspective of the user. A very simplified and focused requirement description." (Pamela Schure & Brian Lawley, "Product Management For Dummies", 2017)
"User stories are short, text-based descriptions of functionality required by a stakeholder group." (Cate McCoy & James L Haner, "CAPM Certified Associate in Project Management Practice Exams", 2018)
"A high-level user or business requirement commonly used in agile software development, typically consisting of one or more sentences in the everyday or business language capturing what functionality a user needs, any non-functional criteria, and also includes acceptance criteria. " (ISTQB)