Rock music is a genre of popular music that originated in the United States in the 1950s. It is characterized by a strong back beat, electric guitars and bass guitar, and often includes keyboard instruments such as the piano or organ. Lyrics are typically focused on themes such as love, rebellion, and social issues. Rock music has evolved over time to include many sub-genres, including hard rock, heavy metal, punk rock, and alternative rock. It is one of the most popular genres of music in the world and continues to influence other styles of music today.