Structure

A structure is a complex data or processing routine, such as a class, trait, interface, function, enumeration.

Structure is an umbrella term to cover all the elements that have a definition, and are used somewhere else in the code. The usage may be name based, or anonymous.

<?php

    function foo() { echo __METHOD__; }

    foo();

?>

See also Understanding All Relations Between Classes, Interfaces, Traits, and Enums in PHP and The difference between Traits, Interfaces, and Abstract Classes in PHP.

Related : Anonymous, Name, Class, Name Conventions