.RELS File Extension
File TypeOpen Office XML Relationships File
What is a RELS file?
File contained within Microsoft Open Office XML documents; contains XML specifications for how "parts" within a "package" are connected to form a document; saved in a _rels directory of an Open Office XML document.
Relationships within RELS files are declared using the XML syntax <Relationship Id="someID" Type="relationshipType" Target="targetPart"/>, where Id is the unique user-defined string, Type is the type of content, and Target is the target file used for the relationship.