Origin: English, Irish
Meaning: the feminine form of Irish name Brian. Of uncertain etymology but may be related to old Celtic element bre meaning "hill" which, by extension, also means "high, noble".
It could also be related to Celtic brig- or brigant- meaning "high" or briga- meaning "might" and "power" or from Celtic brigh- meaning "noble, strong, virtuous".
Briana is a character in The Faerie Queen, an epic poem written by English poet Edmund Spenser, an allegorical work celebrating the rule of Queen Elizabeth I. It was published between 1590 and 1596 though he died before he could finish the entirety of the poem, though it's still considered one of the longest poems in the English language.