What is a dryer on an air compressor?

Compressors from Bambi Air come with two options, with and without a drying column.

As air travels though the hot moving parts of the compressor pistons making its way to the air receiver tank the hot air creates condensation on the walls of the cooler reservoir tank over time building up water that then passes into the airlines being used by the equipment attached.

A drying column cools and dries the air stopping condensation from reaching the main reservoir tank, keeping the stored air in a dry environment.