1. The use of a device with blades that cut vertically into the turf canopy to sever lateral stems, thin grass and dethatch. Also known as verticutting.
2. The thinning of turf grasses by blades or wire tines which cut perpendicular to the soil surface. Specifically designed to remove mat, thatch, and grain from putting greens; to thin dense turf.
This image is an example of what a vertical mower looks like.