A lamia (alternatively, a naga) is a monster girl whose upper body is human and whose lower body is snake-like. Despite having different cultural origins, the two are rendered so similarly as to make it merely a matter of style which one a serpent-legged character will be called.
The term naga comes from Hinduism and Buddhism, and literally means "cobra". Naga can appear with varying degrees of humanity, but typically have fully human torsos. The term lamia comes from Greek, though its original usage did not possess snake-like qualities. It was only in the 1600s that Robert Burton ascribed the familiar qualities, which were subsequently popularized by John Keats in his poem lamia, published in July 1820.
The Japanese, apparently not having either of these myths as a major part of their tradition, tend to ascribe lamia/naga with personalities like those they associate with snakes in general and lamia are often the tsundere types.
