A geared column is a tripod centre column where the height can be adjusted by a flip-out handle – you turn the handle to wind the column up and down. This is slower than a regular centre column, but much more precise, and useful for architectural or still life photography, where the camera position often needs very small, fine adjustments.
With a regular centre column you simply loosen a clamp and slide the column up and down. It’s fast, and better suited to most photographic needs, but it’s also less precise.