A Buddha (also tathāgata, "thus-gone-one") is a being who has achieved enlightenment by understanding the nature of suffering to the very end, and as such is free from the cycle of rebirth.
Also refers to the historical Buddha, Siddharta Gautama (Shakyamuni); or any other notable Buddhas such as Amitabha (Amida), Vairocana or the Medicine Buddha.