Literally, it means "in the style of the church." Since instruments were not permitted in church music during the Middle Ages or Renaissance periods, this term became a synonym for "without instruments" or voices alone. The Renaissance was often referred to as "the golden age of a cappella music." ( Lesson 5, Page 1) HEAR IT
The term is pronounced "ah kah-PEH-lah." The literal translation is "as in church." What it means (and has meant for centuries) is to sing without instrumental accompaniment. It was customary to have unaccompanied singing in many European churches.
A cappella music is vocal music or singing without instrumental accompaniment, or a piece intended to be performed in this way. A cappella is Italian for like in the chapel (music); the term is due to the fact that Christian churches sang without instrumental accompaniment for the first several hundred years of its existence. It is often misspelled as acapella or a capella, which is derived from the Latin spelling (but in Latin capella means small goat).
A Cappella is a 1985 album by Todd Rundgren. The album is one of Rundgren's most unusual in that every sound is the product of the artist's voice. Though it's presented in the conventional way on most songs, all accompanying music comprises vocal-overdubs that are often electronically manipulated and/or looped in order to mimic conventional rock instruments, handclaps, and other various sounds.