**How many of a thing there are, basically.** "Cardinality" refers to the number of elements in a set or other grouping. It's a term commonly used in Data Science to refer to number-of-instances constraints between entities sharing a given relationship in an [[Entity-Relationship Diagrams]]. In mathematics, cardinality refers to the number of elements in a bound set. The set "1, 2, 3, 4, 5, 99" has a cardinality of 6. Note "Cardinality" is not "[[Arity]] ". [[Cardinality is Always One of the Most Important Architectural Decisions]]. Not sure what this is from anymore... but a related graphic showing one particular notation for cardinality: ![[23C6C58B-4689-4902-A1C8-E395C238B87A.jpeg.jpeg]] **** # More ## Source [define cardinality - Google Search](https://www.google.com/search?q=define+cardinality&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari) ## Related - [[Arity]] - [[Relational Databases]] - [[Entity-Relationship Diagrams]] - [[Cardinality is Always One of the Most Important Architectural Decisions]]