Your "zone" is a reference to geographic regions of plant hardiness. This is based the average annual minimum temperatures in your area. There are 11 hardiness zone in north america; zone 1 being the coldest with minimum temperatures reaching -50°f, and zone 11 being the warmest with minimum temperatures never going below 40°f. Plant hardiness is rated by the lowest temperature at which the plant can survive. The USDA map of hardiness zones allows you to click on your area to find your zone and a list of the lowest temperatures that can be expected.