The crossword solution for the term LEAD-IN FOR LA LA is TRA. This is an abbreviation of the word 'TRANSITION, ' which is a musical term used to describe a short passage of music that leads into another section of a song or piece of music. It is often used to bridge two different sections of a song, such as the verse and chorus. The term 'La La' is often used to refer to a vocal improvisation, so the lead-in for La La would be a TRANSITION that leads into the improvisation.