Fringe science refers to ideas whose attributes include being highly speculative or relying on premises already refuted. The chance of ideas rejected by editors and published outside the mainstream being correct is remote. When the general public does not distinguish between science and imitators, it risks exploitation, and in some cases, a "yearning to believe or a generalized suspicion of experts is a very potent incentive to accepting some pseudoscientific claims".

The term "fringe science" covers everything from novel hypotheses, which can be tested utilizing the scientific method, to wild ad hoc hypotheses and mumbo jumbo. This has resulted in a tendency to dismiss all fringe science as the domain of pseudoscientists, hobbyists, and quacks.

A concept that was once accepted by the mainstream scientific community may become fringe science because of a later evaluation of previous research. For example, focal infection theory, which held that focal infections of the tonsils or teeth are a primary cause of systemic disease, was once considered to be medical fact. It has since been dismissed because of a lack of evidence.

The boundary between fringe science and pseudoscience is disputed. Friedlander writes that there is no widespread understanding of what separates science from nonscience or pseudoscience. Pseudoscience, however, is something that is not scientific but is incorrectly characterised as science.

The term may be considered pejorative. For example, Lyell D. Henry Jr. wrote, "Fringe science [is] a term also suggesting kookiness."

Continental drift was rejected for decades lacking conclusive evidence before plate tectonics was accepted.

The confusion between science and pseudoscience, between honest scientific error and genuine scientific discovery, is not new, and it is a permanent feature of the scientific landscape .... Acceptance of new science can come slowly.

Some historical ideas that are considered to have been refuted by mainstream science are: