Glossary
MOND - MOdified Newtonian Dynamics

MOdified Newtonian Dynamics has been proposed as an alternative to non-baryonic Dark Matter. Instead of postulating particles we have not (yet ?) been able to detect, MOND suggests that while the standard dynamics associated with Newton's Laws hold well on familiar scales (ie Solar system type objects/motions), they may may in fact only be approximations of the true laws on the scales of galaxies and beyond.

At the current time, this is not generally accepted, and you will not be examined on the details, unless explicitly told. However frankly MOND is no more radical than the more popular (invisible) "dark matter" hypothesis.