RBB is the fifth Korean extended play and the eighth overall by South Korean girl group Red Velvet. The six-track EP was released on November 30, 2018, by SM Entertainment with iriver and Dreamus as the domestic distributor. Musically, the EP consists of five new original tracks which varied in different genres, mostly R&B and dance-pop, which became the group's third major release to focus on their "Velvet" sonic concept, following their second EP The Velvet (2016), their second studio album Perfect Velvet (2017) and its repackage The Perfect Red Velvet (2018). Upon its release, RBB received positive reviews from music critics for its sonic cohesiveness, how all of the songs in the album are equally "strong" and hailed as the group's most "sassiest offering". The extended play was a commercial success in South Korea, becoming the group's tenth top-three title on the Gaon Album Chart with just one day of tracking. It debuting atop the Top Heatseekers Album chart and became the group's third number-two entry on the Billboard World Albums chart. The lead single "RBB (Really Bad Boy)" was characterized as an R&B pop dance track with a catchy melody. The song was written and composed by SM Entertainment songwriter Kenzie and co-composed by Timothy 'Bos' Bullock, Sara Forsberg, MZMC with arrangement by Bullock. Lyrically, it expresses the charms of a "bad boy". The second song "Butterflies" was described as a punk-pop track, its lyrics comparing the sensation of falling in lov