Unlike pseudo-science, it still uses the scientific method, but is highly speculative.
Fringe science has its basis in established science, but explores and studies areas at the very boundaries, and is often poorly funded and under-resourced.
Whilst fringe science usually leads upon a road to nowhere, occasionally a branch blossoms into a fully established field, and may even bring about a paradigm shift.
Fringe scientists are usually starved of funding, so researchers have the image of the 'eccentric scientist' working away in his shed.
Chaos theory operated at the fringe of accepted physics, using computers and technology begged, borrowed or stolen from other departments. The young scientists who worked upon it were told that they would have trouble finding funding, that other physicists would refuse to review their work, and that they would never move upwards.
Fortunately, they persevered and arrived at a theory, which is widely accepted as having some basis. This is due, in part, to its interdisciplinary nature, which allowed the new science to blossom.
Whilst most scientists regard colleagues working around the fringes of the established order as mavericks, or sometimes a little crazy, it has been argued that they are the force behind scientific change.
Wegener, with his theory of Continental Drift, was subjected to some vituperative attacks, but his theory eventually became a new paradigm.
Whilst astrology is regarded, by modern scientists, as a pseudoscience, this was not always so.
At the time, it was the best model that the ancients could devise from their observations, and they devised some extremely precise measurements for predicting celestial motion.
Astrology eventually developed into a genuine science, astronomy. In the same way, alchemy metamorphosed into chemistry and it can be argued that many 'complimentary' medicines are developing into genuine areas of scientific research.
It would be unfair to call ancient astronomers or alchemists, with their meticulous observations, unscientific, so the term protoscience is used.
Fringe sciences often turn out to be protoscience, the start of a new branch or field of research. Unfortunately, they can just as easily move into the realm of pseudoscience.