Jan (name) – Wikipedia

Jan is a form of John that is used in various languages. The name is used in Afrikaans, Belarusian, Circassian, Catalan, Cornish, Croatian, Czech, Devon dialect, Dutch, German, Kazakh, Polish, Slovak, Slovenian, Scandinavian and Finnic languages. It is the most prevalent in Czech Republic. In English, the name “Jan” is unrelated to “John”, but is a shortened form of the first names Janice, January or Janet, with corresponding pronunciation. It has a separate origin in Persian, Greek, and Armenia

https://en.m.wikipedia.org/wiki/Jan_(name)