"A database or a database object that can be identified by a unique ID and that is backed by database pages." (Karen Paulsell et al, "Sybase SQL Server: Performance and Tuning Guide", 1996)
"An entity is a real-world object, referred to by a noun (person, place, thing, or idea), such as people, products, shipments, cities, and so on. Entities are semantic objects used in English Query." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)
"The main object in an entity-relationship model, which can be deduced by case study examination. Entities represent the things, places, people, concepts, and things involved in a real-world situation, and contain within them properties or attributes that relate to them." (Thomas Moore, "EXAM CRAM™ 2: Designing and Implementing Databases with SQL Server 2000 Enterprise Edition", 2005)
"An object in our logical model that is used to store information about a 'thing of interest'." (Marilyn Miller-White et al, "MCITP Administrator: Microsoft® SQL Server™ 2005 Optimization and Maintenance 70-444", 2007)
"An encapsulation of data that is recognized by a business domain expert as a thing. Logical data entities can be tied to applications, repositories, and services and may be structured according to implementation considerations." (David Lyle & John G Schmidt, "Lean Integration", 2010)
"(1) An element or set of elements that has a distinct, separate existence, although it need not be a material existence. (2) An abstraction from the complexities of some domain." (International Qualifications Board for Business Analysis, 2011)
"Something that exists and is capable of being described. It is a person, place, thing, concept, or event about which your organization maintains facts." (Craig S Mullins, "Database Administration: The Complete Guide to DBA Practices and Procedures" 2nd Ed., 2012)
"An information structure that represents the data characteristic of an entity." (Microsoft)
"An encapsulation of data that is recognized by a business domain expert as a thing. Logical data entities can be tied to applications, repositories, and services and may be structured according to implementation considerations." (TOGAF)