Define "Invasive"

As an example, I have roses, lilacs and Trumpet Vines that send out suckers.
We mow over them or dig them out and give them away/throw them away.
I have English Ivy I cut off whatever growth I don't want.
I have Virginia Creeper all over my garage and adjoining chain link fence and love it.
So what is invasive to one might not be invasive to another....so how can we go on what others might consider invasive that we might not (or vise versa)?
Your thoughts?

My idea of invasive is a plant that is not native to N.America and reseeds itself here constantly. But, just because a plant is not native doesn't mean that it is invasive. As long as it behaves itself and does not spread everywhere over a long period of time it is not invasive.
There are many native plants that are weedy like sweetgum, black cherry,and virginia creeper. While they may be a nuisance, they are not invasive because they were not put here by humans. They naturally existed. If you want to know if a certain plant is invasive, check out where it's native to. If it's from Asia or Europe and is very weedy, it is probably invasive.

Cottage_Rose:

Take a read over on this link: http://davesgarden.com/forums/t/575124/

Weedy (as in, you don't like where it is growing in your garden) doesn't equal the classic definition of invasive. An invasive species is not termed weedy on purpose. An invasive species changes some aspect of the system it invades. That could be chemically, hydrologically, nutritionally, fire-aspect, etc. Note that the behavior of any one plant can and will vary from region to region. That DOES NOT lessen its designation as invasive, however, especially since gardeners are famous for sending plants far and wide. There is some responsibility inherent in raising plants (just as in raising kids and pets).

I look forward to your comments after reviewing the link above.

Once at the link below-
http://www.centerforplantconservation.org/invasives/

please click on the link for the St Louis declaration after you are at that site. This should help you considerably. For some reason the links are broken again and not displaying at the other thread.

A plant that spreads alot, takes over a yard, and is a pain in to control is not necessarily invasive... the correct term for that type of plant would be aggressive.

Invasive plants are plants that do harm to natural ecosystems or cause agricultural damage.

I've said this before... I think when we misuse the term invasive when referring to aggressive plants we trivialize the damage that the true invasives do....

Each state has a list of invasive plants that have been determined to cause real damage to crops or natural habitats. In most states, its illegal to sell, propogate or even grow plants that are listed on the invasive list. Some states are better enforcing their invasive laws than others.

Many groups offer invasive watch lists, a watch list for plants that have not legally been deemed invasive by the government but will probably be legislated in the future.