Structure is a fundamental and sometimes intangible notion covering the recognition, observation, nature, and stability of patterns and relationships of entities. From a child's verbal description of a snowflake, to the detailed scientific analysis of the properties of magnetic fields, the concept of structure is an essential foundation of nearly every mode of inquiry and discovery in science, philosophy, and art.

A structure defines what a system is made of. It is a configuration of items. It is a collection of inter-related components or services. The structure may be a hierarchy (a cascade of one-to-many relationships) or a network featuring many-to-many relationships.

Biological structure

main: Systems biology

In biology, structures exist at all levels of organization, ranging hierarchically from the atomic and molecular to the cellular, tissue, organ, organismic, population and ecosystem level. Usually, a higher-level structure is composed of multiple copies of a lower-level structure.

Chemical structure

main: Chemical structure

Chemistry is the science treating matter at the atomic to macromolecular scale, the reactions, transformations and aggregations of matter, as well as accompanying energy and entropy changes during these processes. The chemical structure refers to both molecular geometry and to electronic structure. The structural formula of a chemical compound is a graphical representation of the molecular structure showing how the atoms are arranged. A protein structure is the three dimensional coordinates of the atoms within (macro) molecules made of protein.

Built structure

A structure usually refers to any large, man-made object permanently fixed to Earth's surface, as a result of construction. These are divided into buildings and nonbuilding structures, and make up the infrastructure of a human society. There are also animal-built structures, such as anthills and beaver dams.

Musical composition

Music is an art form consisting of sound and silence expressed through time. The term musical form, a type of structure, refers to two related concepts:

• the type of composition (for example, a musical work can have the form of a symphony, a concerto, or other generic type)
• the structure of a particular piece (for example, a piece can be written in binary form, sonata form, as a fugue, etc.)

Social structure

main: Social structure

A social structure is a pattern of relations. They are social organizations of individuals in various life situations. Structures are applicable to people in how a society is as a system organized by a characteristic pattern of relationships. This is known as the social organization of the group. Sociologists have studied the changing structure of these groups. Structure and agency is the two confronted theories about human behaviour. The debate surrounding the influence of structure and agency on human thought and behaviour is one of the central issues in sociology. In this context "agency" refers to the capacity of individual humans to act independently and to make their own free choices. "Structure" here refers to those factors such as social class, religion, gender, ethnicity, customs etc. which seem to limit or influence the opportunities that individuals have.