Bajosexto

A bajo sexto is a musical instrument with 12 strings in 6 double courses, used in Mexican music. It is used primarily in norteño music of northeastern Mexico and across the border in the music of south Texas known as "Tex-Mex," "conjunto," or "música mexicana-tejana". A five course version of the bajo sexto has appeared in recent years in response to players removing the final E course, which they feel muddies the sound too much. Unsurprisingly, it's called the bajo quinto.
The bajo sexto sound provides a strong rhythm in the lower pitched end of a Conjunto or Tejano band and also provides a strong projection of chord changes across songs.