If one has some data that needs to be sorted or indexed, the key is the part of the data that is used to make comparisons (if sorting) or to enter into the .

For example, if one has a list of people the in the data might be names and addresses. One might sort by last name as a key or by street address as another key.

Title key
Canonical name Key
Date of creation 2013-03-22 17:22:21
Last modified on 2013-03-22 17:22:21
Owner Mathprof (13753)
Last modified by Mathprof (13753)
Numerical id 5
Author Mathprof (13753)
Entry type Definition
Classification msc 68P10
Classification msc 68P05