For our region a native plant is one that has evolved in the Piedmont, Eastern Deciduous Forest or Coastal Plain. The literature will help you choose plants appropriate to your exact location.
Our committee has been debating a question regarding how to take climate change (changing USDA Plant Hardiness Zones) into account. Our consensus was that the native plants favored for “promotion” should be those which have wide ranges. In other words, favored plants would be those that are native to our area and current zone, but are also native to areas and zones to the south. The limiting factor in the ability of a plant to spread north as the climate zones change will be soil type.
If at all possible, try to choose plants that are not cultivars in order to protect the biodiversity of the species and to support native pollinators who do not recognize cultivars (a cultivar is a plant whose characteristics are selected and bred by humans) or hybrids as food and/or nesting sources.
Terms used locally:
Bay-wise: Used by Master Gardeners
Bayscape: Used by NOAA
BaySafe: Used by Benhke's Nursery, but they apply this to cultivars and hybrids as well as non-cultivars and non-hybrids, so be sure to ask if you want the most benefit of pollinators.
Rainscapes: Montgomery County's watershed landscaping term.
Please be mindful of words like "weed" and "pest".
The word "weed," as brought to us by our European ancestors, meant any plant that was not a "European" ornamental. Thus most Native American plants were wild weeds to be rooted out of our gardens. This is one possible cause of the decline and/or extinction of many native species.
Our current working definition is any non-native, invasive species that out-competes the natives. Many of these are currently sold in garden stores, such as Vinca or English Ivy. Examples of non-natives that have become truly invasive are kudzu, Japanese stilt grass, dandelions, etc.
The word "pest" was any insect that ate our ornamental plants. Now we know that in a biologically diverse yard, in order to have pollinators and their larvae, we need to get used to insects munching on the plants. It's the right and proper order of things. Therefore an insect only becomes a pest if it is out-competing other insects or causing so much damage that the plants can't recover.
A word of caution: not all "experts" are trained to recognize the difference between a native plant that has volunteered itself in
your yard and a non-native "weed."