I find it is generally used to describe things that are getting out of hand. Often invasive species thrive because there's no natural predation or check and balance for some reason.
Most of the species in my garden are non-native (another term that is often used for less virulent invasives), but they don't colonize the native landscape. The term "invasive" is sometimes used for plants that could otherwise be fine, but will get out of hand in some cases. Bamboo, for instance.
Source: none, but I used to take care of shrubbery for one of my first jobs and I learned a lot about invasives. I hated Brazilian pepper trees the most ( https://en.wikipedia.org/wiki/Schinus_terebinthifolia ), mainly because they're quite difficult to remove.
Most of the species in my garden are non-native (another term that is often used for less virulent invasives), but they don't colonize the native landscape. The term "invasive" is sometimes used for plants that could otherwise be fine, but will get out of hand in some cases. Bamboo, for instance.
Source: none, but I used to take care of shrubbery for one of my first jobs and I learned a lot about invasives. I hated Brazilian pepper trees the most ( https://en.wikipedia.org/wiki/Schinus_terebinthifolia ), mainly because they're quite difficult to remove.