You can be forgiven for not knowing... I didn't either until a couple of weeks ago. It is a particular kind of guitar which has an unusual configuration of strings, probably evolved from the Spanish guitars brought over by the conquistadors. You can read more about it here: Tiple
The instrument is about two-thirds the size of a standard guitar, unless it is something that has been created by some of the more enthusiastic tiple players, in which case the instrument might have been redesigned to accommodate electric formats. (See the concert photo below.)
The Tiple artist is usually a man, although there is a woman living in Barichara, now elderly, who was nationally recognized for her Tiple performances. One clue as to the kind of guitarist you are meeting is that it is not common, I was told, for a Tiple player to shake hands, especially with a man, because their hands must be exceptionally agile to play the notes as rapidly as they do and if a handshake is too harsh, it could mean a negative affect on a performance. The hands will feel soft, but muscular and the nails on the right hand are longer to provide the picking sound.
Here is a link to an Andes website - Folklore Los Andinos - where you can see pictures of the instruments, more details and hear some music.
Recently at the Casa de Cultura in Barichara a concert was held to hear Javier Enrique Gomez Noriega play a variety of Tiple songs. I readily admit I am no expert on guitar, much less on tiple. But seeing how much skill is required to play ALL 12 of the strings (and sometimes it evens seems as if they are all being played at once) you can appreciate what a real art form this musical effort is. What is also remarkable is that most Tiple players can play a musical line with both hands, first from the right hand and then repeated in a different octave with the right playing off the fret itself, making the strings of the guitar work through an incredibly wide range of notes.
You can see an example of tiple with Javier playing on the video link through YouTube below. I apologize in advance that the video is less than perfect. The lighting was terrible and I didn't have a front row seat. http://www.youtube.com/watch?v=Zc_Zp3Grv_0
When Javier heard that I was writing a blog about tiple, he asked that I include his email address so that he can answer questions (firstname.lastname@example.org) and if you would like to talk to him in Spanish, he is willing to receive calls as well. I have his phone number, so you can send me a request and I will pass it on to you.
There is one snippet of the group shown here playing during the 1er Festival de Musica Barichara at this site: http://www.facebook.com/video/video.php?v=10150153538245031&comments but it's not a great presentation, really. But you get a hint of what the music sounds like.