The bajo sexto (sixth bass in Spanish), and the bajo quinto are Texan and Mexican musical instruments that belong to the guitar family. The bajo sexto has six choirs of two strings which make it strongly related to the twelve string guitar. The bajo quinto has only five choirs and is, in a way, a bajo sexto with the lowest string choir removed.

Since the middle of the twentieth century, the bajo sexto has become an emblematic instrument of norteña music, more particularly of the norteño style, and with the accordion, of mexicanity. It is also used, to a lesser extent, in the traditional music of the states of Oaxaca and Puebla. It should not be confused with the guitarron, the bass guitar characteristic of mariachi bands.

https://fr.wikipedia.org/wiki/Bajo_sexto_et_bajo_quinto

https://en.wikipedia.org/wiki/Bajo_sexto

https://es.wikipedia.org/wiki/Bajo_sexto

While technically bajo sexto and bajo quinto look like 12 strings and 10 strings guitar, they are tuned and played differently from guitars. Bajo Quinto is somewhat technically a bajo sexto whose two bass strings have been removed. Nevertheless they are used by different styles of music "bajo quinto" is used with different tunings in "musica mixteca" and "mexican norteño music" and is used for playing melody and its decoration. "Bajo sexto" is used by traditional "Mexican norteño music" and traditional tex-mex music as a rhythmic instrument. So when mentioned "bajo sexto" and "bajo quinto" are great filters for identifying the real style of musical recordings.