"Do Re Mi" refers to the solfège system, a method used to teach pitch and sight-singing in music. The syllables Do, Re, Mi, Fa, Sol, La, and Ti represent the seven notes of the major scale. This system helps musicians understand musical intervals and improve their vocal skills. The concept gained popularity through the song "Do-Re-Mi" from the musical The Sound of Music, written by Richard Rodgers and Oscar Hammerstein II. In the song, the syllables are associated with various objects and ideas, making it easier for children to learn music fundamentals in a fun and engaging way.