They were a group of pious, well learned Chasidim who most of them lived or learned in the Hungarian Shtetel Nyírvasvári (Oshvar in Yiddish). They were know for their tremendous piety an were know to be well versed in the Kabalistic works of Rabbi Issac Luria (the Arizal) (See Sefer Heichal Habracha from Rabbi Issac of Komarno parashat Matos)
Thus they were called Chasidei Aish V’oR (a wordplay based on the name of the Shtetel) literally meaning Fire and Light (translation from Hebrew).
A big influencer of the group was Rabbi Yitzchak Issac Taub of the Kaliv dynasty.
I hope this information helps,