In Spanish the word cola means the “tail” which corresponds exactly with its meaning in the mezcal world where it refers to the final, highly volatile, component of the distillation.
When alcohol is distilled the liquid that comes out of the still is divided into three parts; the beginning, middle, and end of each distillation. The distilling world generally refers to these as the head, heart or body, and tail of a distillation run. In Mexico they are referred to as the puntas, cuerpo or corazón, and colas. Each contains different chemicals with the most toxic components concentrated in the head and tails. Generally this means that distillers cut out the heads and tails to keep only the body. Outside of the mezcal world, methanol is generally concentrated in the heads of a distillation so it’s common to just cut that out of the final product.
Colas are rarely bottled on their own because they have so little alcohol and tend to be so volatile. A small portion is frequently blended into a mezcal in order to balance out flavors or the final ABV.