"MODS is an XML schema for a bibliographic element set that may be used for a variety of purposes, and particularly for library applications. It is a derivative of the MARC 21 bibliographic format (MAchine-Readable Cataloging) and as such includes a subset of MARC fields, using language-based tags rather than numeric ones. Definitions (semantics) of MODS elements may be found in the appropriate section." -- Definition taken from MODS User Guidelines Version 3 by the Library of Congress
Examples of MODS records can be found here
Element: <titleInfo>
Definition: A word, phrase, character, or group of characters, normally appearing in a resource, that names it or the work contained in it.
Subelements: <title> <subTitle> <partNumber> <partName> <nonSort>
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Element: <typeOfResource>
Definition: A term that specifies the characteristiscs and genearl type of content of the resource.
Subelements: None
Values: A list of values for this field can be found at: http://www.loc.gov/standards/mods/userguide/typeofresource.html
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Element: <originInfo>
Definition: Information about the origin of the resource, including place of origin or publication, publisher/orgininator, and dates associated with the resource.
Subelement: <place> <publisher> <dateIssued> <dateCreated> <dateCaptured> <dateValid> <dateModified> <copyrightDate> <dateOther> <edition> <issurance> <frequency>
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Element: <language>
Definition: A designation of the language in which the content of a resource is expressed.
Subelement: <languageTerm> <scriptTerm>
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Element: <physicalDescription>
Definition: Describes the physical attributes of the information resource.
Subelement: <form> <reformattingQuality> <internetMediaType> <extent> <digitalOrigin> <note>
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Element: <subject>
Definition: A term or phrase representing the primary topic on which a work is focused.
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Element: <location>
Definition: Physical location.
Subelement: <physicalLocation
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Element: <accessCondition>
Definition: The level of access allowed to an entity.
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Element: <recordInfo>
Definition: Provides additional information about the record.
Subelement: <recordContentSource> ; <recordCreationDate> ; <recordChangeDate> ; <recordIdentifier> ; <recordOrigin> <recordInfoNote>