She is talking about plant hardiness zones. The U.S. is divided into zones based on climate, which helps gardeners know which plants are best for their areas. Plants that grow wonderfully in Ohio probably won't be good to plant in Arizona.
Here's a link:
https://planthardiness.ars.usda.gov/
Type your zip code in the box on the upper right and a little drop-down box will tell you which gardening zone you are in.