In the case of a library catalogue you are providing information about a document that exists in the library. This means you are preparing an entry for the document. S.R. Ranganathan defined an entry as 'ultimate unit record in a catalogue or documentation list'.
In a library catalogue entry the information provided may be elaborate or very brief What information is to be given, how much of it should be given, and how the information is to be given are decided according to the need and purpose of a particular catalogue entry.