The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomers, and in software for easily calculating elapsed days between two events. Wikipedia

The continuous count of days since the beginning of the Julian Period Wikipedia Disambiguation

A continuous sequential count of days since day 0 at the beginning of the Julian Period on Monday, January 1, 4713 BC, proleptic Julian calendar Wikipedia Disambiguation

Days since the beginning of the Julian Period Wikidata

A date expressed as a real number of days counted with GMT noon on 1 January 4713 BC in proleptic Julian calendar (November 24, 4714 BC, in the proleptic Gregorian calendar) as zero; used primarily by astronomers and historians to compare events recorded in different cultures . Wiktionary

Date. Wiktionary (translation)