empty

Empty is an adjective and noun that denotes the absence of content, occupants, or substance. In everyday use it describes containers or spaces that hold nothing, such as an empty bottle or an empty room. The term is often relative: something may be described as empty only in comparison with a fuller or more occupied state. Common expressions include “empty-handed” and “empty space.”

In mathematics, the concept is formalized as the empty set, the unique set containing no elements. The empty set, denoted ∅ or {}, is a subset of every set and has cardinality zero. It serves as a neutral element for union and as the starting point for many proofs, and statements about intersections with the empty set yield the empty set.

In computing and data contexts, empty denotes the absence of data. An empty string is a string of length zero; an empty list or array contains no elements. Databases differentiate empty (or null) values from zero or an empty string, reflecting different kinds of absence that affect processing and queries.

Physically, “empty space” or vacuum is not truly empty. Quantum field theory describes fluctuations and vacuum energy; what appears empty on macroscopic scales may teem with transient activity at small scales.

Philosophical and cultural usage often treats emptiness as a fundamental property. In Buddhism, emptiness (śūnyatā) denotes the lack of inherent, independent existence of phenomena and encourages a view beyond solid contrasts. In everyday nutrition, “empty calories” refer to energy sources with little nutritional value.