The term 'smooth musical passage' can be described as a LEGATO, which is a musical term that refers to the smooth and connected playing of notes. LEGATO is derived from the Italian word for 'tied together, ' and it is used to describe a style of playing in which the notes are connected without any breaks or pauses. This type of playing creates a smooth and continuous sound, which is why it is often used to create a more lyrical and expressive musical passage.