A monster girl whose upper body is human and whose lower body is snake-like. Lamia and naga are often rendered so similarly as to make it merely a matter of style which one a serpent-legged character will be called.
Mythologically, lamia (wikipedia link) are from Greek myth - The lamia was created by Hera. A Lybian queen was raped by Zeus. Since Hera couldn't punish her husband for his cheating, she decided to murder the queen's children in front of her, then turned the queen into a part-serpent monster so that she would be shunned. Hera also cursed her to eat other children.
Naga (Wikipedia link) are from Hinduism and Buddhism, and literally means "cobra". They can appear with varying degrees of humanity, but typically have fully human torsos in fanart because that's sexier. Naga have traditionally been seen as friendly to humans, with even having cobra-like naga sheltering Buddha himself from rain as he meditates in some iconography.
Although naga are more appropriate for the friendly roles, sword-and-sorcery settings tend to call serpentine girls lamia.
The Japanese, apparently not having either of these myths a major part of their tradition, tend to ascribe lamia/naga with personalities like those they associate with snakes in general - especially big egos - and lamia are often the tsundere types. They also tend to have snake-frog-slug jokes.
- Alipheese Fateburn XVI from Mon-Musu Quest!
- Cassiopeia Du Couteau from League of Legends
- Deis from Breath of Fire
- Echidna from Granblue Fantasy
- Echidna from Puzzle & Dragons
- Isis from Ragnarok Online
- Jashin-chan from Jashin-chan Dropkick
- Kagome Ririko from Rosario+Vampire
- Kiyohime from Fate/Grand Order
- Lamia Hygieia from Mamonomusume to no Seikatsu
- Miia and her mother from Monster Musume no Iru Nichijou
- Saphentite Neikes from Monster Musume no Oisha-san
- Tuki from Shantae: Half-Genie Hero