The word schema comes from the Greek word "σχήμα" (skhēma) that means shape or more generally plan.

The Greek plural is "σχήματα" (skhēmata). In English literature, both schemas and schemata are used as the plural form of "schema".

The word schema can represent any of several different things:

1. In computer science, a schema is a model.
2. In formal logic, a rule (usually recursively definable) describing a set (usually infinite) of statements. For example, the axiom schema of replacement is a schema of axioms in axiomatic set theory.
3. A description of the structure of a database; or: a defined part of a database. See software architecture, conceptual schema, Sowa's conceptual graph, semantic network, Berners-Lee's semantic web.
4. An XML schema provides a means for defining the structure, content and to some extent, the semantics of XML documents.
5. Part of a formal specification written in the Z specification language.
6. A minimal and specialized ontology, i.e., a list of questions, answers to which describe what exists in the world. This includes only what is required for some narrow range of actions; e.g., a library card catalogue schema asks librarians only to provide enough information about the book to help library users decide if they want to browse through it, and if so, how to find it. By contrast, an ontology enables a much broader range of actions, e.g., all of those normally associated with a working trade or profession.
7. Schemas also are very important in the field of psychology, especially concerning educational practices.
8. In genetic algorithms or genetic programming A set of programs or bit strings that have some genotypic similarity. Usually the set is specified by defining a similarity template which members of the set must match. The template specifies the fixed part, which the programs must match, and the variable part. Don't care symbols are used to define the variable part. In tree schemata, both the content and the shape of the tree must be considered. See also : Defining Length, Disruption, Effective fitness, Length of a schema, Order, Wild-card symbol
9. In psychology or Theory of Cognitive development or Schema (psychology) A mental set or representation. The mental representation of a concept can be assimilation to match an existing schema (representing the concept according to a preexisting schema), or accomodation (modifying an existing schema to adapt to the environment.
10. The Schema and the Great Schema (Μεγαλοσχήμος) are part of the monastic attire of advanced monks and nuns in the Eastern Orthodox Church.

See also scheme.