The term IMPROVISE AS A VOCALIST can be summarized as a job description for a vocalist who is able to create and perform music spontaneously. This type of performance is often referred to as SCAT singing, which is a four-letter word that is also a solution to the crossword. SCAT singing is a form of jazz singing that involves improvisation with nonsense syllables, words, and phrases. It is a popular style of singing that requires a great deal of skill and creativity.