While the origin of the name 'Taira' is unknown, the most influential theory proposed by Akira OTA and developed by Kunihiko FUJIKI, Arikiyo SAEKI and others, states that "Taira" derives from a Japanese reading of the kanji character "平" in "平安京," the ancient capital in present-day Kyoto which was built by the Emperor Kanmu, an ancestor of the first Taira clan, Kanmu-Heishi.
「平」という名称の由来は不明であるが、もっとも有力な説は太田亮が唱えて藤木邦彦・佐伯有清らが発展させた説で、最初の平氏であった桓武平氏の祖である桓武天皇が建設した平安京にちなんで「平（和訓多比良）」と名づけたとするものである。