in dating terms, a repeating cycle of 15 years beginning on 1st September 312, introduced by the Emperor Constantine for taxation purposes but utilised as a dating system during the medieval era
Starting in the middle ages, a term used to indicate a 15-year taxation cycle. It had no astronomical significance.
An indiction is any of the years in a 15-year cycle used to date medieval documents. Each year was numbered: first indiction, second indiction, etc. However, the cycles were not numbered, thus other information is needed to identify the specific year.