BB stands for Blemish Balm or Beauty Balm. BB cream is a skincare/makeup hybrid that provides the hydration of a moisturizer, and the coverage of a light foundation. The texture is creamier than most tinted moisturizers and BB creams generally offer more coverage than tinted moisturizer (though less than foundation).
This multitasking cream streamlines the process of makeup application. If one is looking for a beauty product that moisturizes your skin and provides light coverage with a matte finish, BB cream is the product that they need.