/ˈmɛtəˌdeɪtə/
noun — "data that describes other data."
Metadata is structured information that provides context, description, or additional attributes about other data. It does not typically contain the primary content itself but conveys essential properties, relationships, and management details that facilitate understanding, organization, retrieval, and processing of the main data. In computing, metadata is widely used in databases, filesystems, web services, multimedia, and distributed systems to enhance data management and interoperability.
Technically, metadata can be categorized into several types: descriptive metadata, which explains the content and purpose (e.g., title, author, keywords); structural metadata, which indicates relationships or formats (e.g., chapters in a document, table schemas); administrative metadata, which supports management tasks (e.g., file size, creation date, permissions); and semantic metadata, which adds meaning or ontological context. In filesystems, metadata includes attributes like creation time, modification time, permissions, and owner, while in web applications, metadata is often represented in HTML <meta> tags or JSON-LD structures for SEO and semantic interpretation.
Operationally, metadata enhances searchability, indexing, and automated processing. For instance, a photo may have embedded metadata indicating the camera model, GPS coordinates, and exposure settings. In databases, indexing fields act as metadata to accelerate queries. In distributed systems, metadata allows systems to track data location, versioning, and replication state, improving consistency and fault tolerance. A practical example in a JSON-based REST API might look like:
{
"data": [...],
"metadata": {
"count": 120,
"page": 1,
"per_page": 20,
"timestamp": "2026-01-31T12:00:00Z"
}
}
This structure conveys contextual information about the main data payload, such as pagination and time of retrieval, facilitating client processing and integration.
In practice, metadata is essential for compliance, digital rights management, security auditing, and automated workflows. Metadata standards like Dublin Core, EXIF for images, and XMP for multimedia files provide consistency across systems and applications, allowing software and humans to interpret data correctly.
Conceptually, metadata is like a library card catalog: it does not contain the books themselves but tells you where they are, who wrote them, when they were published, and what subject they cover, enabling efficient access and understanding.
See Digital Watermarking, LSB, Database, FileSystem, Index.