Noun. 1. col-a pass between mountain peaks. gap.mountain pass, notch, pass-the location in a range of mountains of a geological formation that is lower than the surrounding peaks; we got through the pass before it started to snow. water gap-a pass in a mountain ridge through which a stream flows.ol. 1. a pass or depression in a mountain range or ridge. 2. the region of relatively low pressure between two anticyclones.