Gubraithian fire (Incantation Unknown), also known as Everlasting fire is a flame which has been enchanted to burn forever without dying. It is quite an advanced piece of magic, as few wizards were capable of it.
Being such an advanced spell, the casting of it was most likely not taught at Hogwarts, though by Harry Potter's fifth year, Professor Flitwick had mentioned it at least twice during his Charms lessons, according to Hermione Granger.
The name "Gubraithian" is probably taken from the Scottish Gaelic phrase "gu brath", which means "forever".
- Harry Potter and the Order of the Phoenix (Mentioned only)