Metadata

A set of data that describes and gives information about other data.

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This is the base class for all metadata types. You cannot edit this object. A component is an instance of a metadata type.

Metadata is analogous to sObject, which represents all standard objects. Metadata represents all components and fields inMetadata API. Instead of identifying each component with an ID, each custom object or custom field has a unique fullName, which must be distinct from standard object names, as it must be when you create custom objects or custom fields in theSalesforce user interface.

for more detail read meta data guide