The New Grove Dictionary of Musical Instruments splits marimba into three parts or types of instruments: (1) the marimbas of Africa and Latin America; (2) the modern orchestral marimba; and (3) the marimbas of Harry Partch. The term is defined as “a group of idiophones, some of which are plucked (lamellaphones) and some of which are struck (xylophones).” It also states that the Latin-American instrument came from Africa.
Since the marimba is generally accepted to be a type of xylophone, that term also deserves further scrutiny. The xylophone article in the New Grove Dictionary was written by Lois Ann Anderson, James Blades, George Kist, and Linda O’Brien. There is much more detail in it regarding the marimba than in the marimba entry (in the same compendium) by Gerhard Kubik, Blades, and Rosemary Roberts.