It signifies the number of columns and how many columns each section, or div, takes. In your example, the first section would take 2 columns out of twelve. The

It signifies the number of columns and how many columns each section, or div, takes. In your example, the first section would take 2 columns out of twelve. The second section takes the remaining 10 columns. Or, col-3-12 & col-9-12; first section would take 3 columns out of twelve and the second takes the remaining nine. What I'm curious about is if doing something like this: col-2-12 & col-8-12. But I'm too lazy to download the css to see for myself.