What Is Love? is the fifth extended play (EP) by South Korean girl group Twice. The EP was released on April 9, 2018 by JYP Entertainment and is distributed by Iriver. It includes the lead single of the same name produced by Park Jin-young. Twice members Jeongyeon, Chaeyoung, and Jihyo also took part in writing lyrics for two songs on the EP.
The reissue of What Is Love?, titled Summer Nights, was released on July 9, 2018.