The Beta is second-in-command to an Alpha in a clique. Whenever the alpha's not around, the beta's the temporary alpha. Although if anything happens to the alpha where they can't be the alpha anymore (like if they get kicked out of the clique by the others members or something), the beta becomes the new official alpha. Alicia Rivera was the PC's beta until Massie Block moved to England, thus making Alicia the new official alpha.