A chronogram is a sentence or inscription in which specific letters, interpreted as numerals

Numeral system

A numeral system is a writing system for expressing numbers, that is a mathematical notation for representing numbers of a given set, using graphemes or symbols in a consistent manner....

, stand for a particular date when rearranged. The word, meaning "time writing", derives from the Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 words chronos ("time") and gramma ("letter"). In the pure chronogram each word contains a numeral, the natural chronogram shows all numerals in the correct numerical order, e.g. AMORE MATVRITAS = MMVI = 2006.