Which term describes the instrumental parts in the bass staff that accompanied a main melodic line in baroque music? basso continuo basso ostinato basso obbligato basso buffo

The answer is basso continuo  

From the Italian language sometimes abbreviated as b.c  is a technique of self-composition and execution and essential  from the Baroque period  

The basso continuo is played for one or various instruments, typically and harmonic as the keyboard instruments or others as the harp or lute  

with the voice of bass simultaneously in charge of an instrument of grave tessitura like the violoncello, bassoon, the viola da gamba, contrabass and sometimes contrabasso.  

It also receives the name of simultaneous accompaniment