
1) Latin phrase
Found on
https://www.crosswordclues.com/clue/floruit

Floruit (t or t), abbreviated fl. (or occasionally, flor.), is a Latin verb meaning `flourished`, denoting the period of time during which something (such as a person, school, movement, or species) was active. In English, the word may also be used as a noun indicating the time when someone `flourished`. Broadly, the term is employed in referen...
Found on
http://en.wikipedia.org/wiki/Floruit

dates of a person's birth and death
Found on
http://phrontistery.info/f.html
(fl) when a historical character was most productive/active - used in biographical information, especially if birth/death dates are unknown, the 'fl' symbol appears with the year(s) of his/her prominence
Found on
https://www.businessballs.com/glossaries-and-terminology/latin-terms-and-ph

he (or she) flourished: used to indicate the period during which a person flourished, esp. when the exact birth and death dates are unknown. Abbr.: fl., flor.
Found on
https://www.infoplease.com/dictionary/floruit
No exact match found.