In a broad sense, pop is any music based on memorable melodies, repeated sections (usually, but not always, verses and choruses), and a tight, concise structure that keeps the listener's focus on those elements. Pop as a musical style, however, began in the late '90s and early 2000s, when a pair of major forces began narrowing and focusing commercial tastes. First, the heavy influence of rap and R&B made the pop singles charts more homogeneous than ever. Then, the advent of the television contest American Idol further centralized what people agreed on as pop music. As such, Pop is primarily influenced by the time's two most broadly popular styles: R&B and adult contemporary.