Falguna (also spelled Phalguna), a spring season month according to Hindu calendar, is origin of this word.
[1][2] Fagu is a lyrical form depicting beauty of nature during spring.
It also portrays joys and pleasures of love, fears and hopes separation and union of lovers.
This form was popular among Jain poets who were mostly monks, so many of these Fagu start with erotic sentiments and ends with renunciation or self restraints.
There are twelve known Fagus of these period and majority of them are written by Jain monks.