Planting Zones are weather regions determined by the lowest recorded temperatures for that area. They are used in gardening to rate plant and climate compatibility.
A numbered scale is used: the lower the number, the colder the region and the hardier the plant required. Knowing which zone you are in enables you to select plants that will thrive in your garden, rather than struggle in an incompatible climate.
Here is a link to a website that talks about planting zones. If you scroll down the page, there is a handy chart that summarizes the zones by temperature:
http://www.lawn-and-gardening-tips.com/planting-zones.html
Here are more helpful links as well:
http://atlas.nrcan.gc.ca/site/english/maps/environment/forest/forestcanada/planthardi
http://www.veseys.com/ca/en/learn/reference/hardinesszones