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Properties and attributes are terms commonly used in computing to describe data about program elements and objects. Their precise meaning depends on the language and domain, but they broadly refer to stateful data (properties) and metadata or declarative information (attributes).

In object-oriented programming languages, a property is a member that provides access to an object's state, typically via getters and setters, and may implement encapsulation, validation, or computed values. In languages like C#, properties are first-class language features. Attributes or annotations are metadata applied to declarations such as classes, methods, or fields. They are inspected at compile time or run time via reflection and can influence behavior of frameworks, serialization, and tooling. Examples include C# attributes like [Serializable], Java annotations like @Override, and Python decorators that attach metadata to functions or classes.

In HTML and the DOM, an attribute is part of the markup that specifies initial values, while the DOM property reflects the current state in memory and can diverge from attributes after scripts change it. This distinction matters for accessibility, scripting, and rendering.

Across domains, users should distinguish between data properties (the actual state of an object) and metadata (information about that data). Understanding the distinction helps avoid confusion when using frameworks that rely on annotations to control behavior or properties to define object state. See also: annotations, decorators, reflection, metadata, serialization, DOM, attributes.