subelement
Technical computing term for a component that is part of a larger element or structure.
In XML, subelements are contained within a parent element.
要素 is a general term for 'element' or 'factor', while 部分要素 specifically refers to a subelement or component within a larger structure, often in computing contexts.
Compound of 部分 (ぶぶん, 'part') and 要素 (ようそ, 'element'). A straightforward technical term.