The term wildflower is not a scientific term. It could mean any species that grows wild in uncultivated areas, or plants that were not intentionally seeded. Basically, it has come to mean that it is a species that is not a hybrid or cultivar (created by humans), and that it grows in the wild as a native plant.
Some wildflowers are actually considered invasive or noxious weeds in certain areas, while in other areas they are considered acceptable flowers. That’s because plants take on different characteristics in relation to the climate and altitude in which they are growing, and the same plant may be considered a wildflower in a colder mountain region and be considered an invasive weed in warmer, lower areas. The reverse could also be true.
Additionally, many plants which are considered wildflowers are actually introduced species, which don’t naturally occur in the region, but which have become naturalized.