The Free On-line Dictionary of Computing (30 December 2018):

periodic group

    (PE) Groups of logically related fields which occur
   multiple times within a group.

   Periodic groups are a non-relational technique.  An example
   of a PE would be for storing the history of a person's name
   changes, where name was kept in logically related fields such
   as surname, first name and middle name - with the person
   having changed their name more than once.

   [Clarification?]

   (1995-10-30)