RBB is the fifth 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 serving as the South Korean distributor. Musically, the EP consists of five new original tracks which varied in different genres, mostly R&B, hip-hop and dance-pop, which became the group's third major release to focus on their "Velvet" sonic concept, following their second studio album Perfect Velvet and its repackage The Perfect Red Velvet. Upon its release, RBB received positive reviews from international 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". Its title track, however, received mixed reactions from the group's native critics and public, whom deemed it "controversial" and "unfamiliar" to the public. 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 tracking day, and became the forty-nine best selling album of 2018 in South Korea by the end of the year. It was a bigger international success for Red Velvet, becoming the group's third number-two entry on the Billboard World Albums Chart and their debuting atop the Top Heatseekers Album chart, earning the group's their best sales week, and to date, their best-selling release in the United States. In continuation to the success of their previous release, RBB was the group's second release to enter the component digital album chart in France and the United Kingdom. To promote the extended play, its eponymous lead single was released on the same physical release date. Though the song received mixed reviews from domestic critics, it was a moderate success on the Gaon Digital Chart, becoming the group's eleventh top-ten hit with just one tracking day. The single, however, attained bigger success both commercially and critically overseas, becoming the group's first number one title on the Billboard World Digital Song Sales.
The song "Sassy Me" was co-written by Dsign Music.