What is a bolo roast.
The information provided by both Paparazzi's answer and logophobe's comment is correct. The bolo is from the forequarter of the cow, specifically from the shoulder area. 

I don't know of one single whole cut in the US that would encompass the whole bolo roast. However, we have three cuts that make up the three primary parts of the bolo roast. 


Round bolo = mock tender roast
Shoulder bolo = shoulder roast
Side bolo = boneless blade roast


This picture shows it quite well. (Cropped to remove ads.)



And this picture shows the three pieces together as a whole bolo roast: