Structured data set at the head of a document, describing it. Frontmatter is for machines; the body is for readers.
Compound of front (Latin frons, brow, foremost part) and matter (Latin materia, substance); structured data set at the head of a document, meant for machines rather than readers.
Structured data set at the head of a document, describing it before the body begins: written for machines, while the body is written for readers.