In "don't worry, be happy," bobby mcferrin sings meaningless syllables called

I believe the answer is vocables.

Vocables usually words that could be referenced to others rather than words that actually have meaning.

Examples of the use of vocables is the useage of 'na' or 'la' that combined with actual words that contain meaning within the song.

In this song, McFerrin's interjection of meaningless syllables is typical of a type of singing known as "scat" or "scatting". this is most commonly used in Jazz music, where the singer fills the space between words with nonsense or meaningless words and syllables. However, this type of singing is not completely without form - the intent is to complement the progression and melody of the accompanying instrumentals.