What is an heirloom seed?

All seeds grown at the farm are open-pollinated heirlooms. 

When I worked with Growing Up Organic, an amazing not for profit organization in the Ottawa area, we developed a school garden guide for teachers and students. In this guide, we wrote a section on seeds - instead of reinventing the wheel, I will share it here.  Some information on the difference between heirloom, open-pollinated, hybrid and genetically modified organisms (gmo) seeds.