Boon is mechanic in some older dungeons.
Boon resurrects all dead party members with 120 stamina and full HP/MP, and fully restores HP and MP to alive members. Novice Boons also provide a few seconds of invincibility to all members. There were usually 3 boons with 3 minute intervals.
Boons did exist in leveling dungeons and circa 2015 in dungeons like BRNM/TSNM/CW/SC. They did not happen in hard mode versions or newer dungeons like KD, FI.
Boons seem to be removed from most dungeons now and replaced with paid resurrection. This mechanic however still exists in level 60 Balder's Temple.