Exotic particle
An exotic particle is a kind of theoretical particle said to exist by some areas of modern physics, and whose alleged properties are extremely unusual.
The best-known example is probably the tachyon, a hypothetical particle that always travels faster than light.
Another example of this is supersymmetry, a theoretical set of significantly heavier versions of known particles (this is also one of the proposed candidates for dark matter).
Exotic particles are frequently featured in science fiction, either those with real-world academic backing, or entirely fictional.
References
Further reading
Ma, Ernest; Raidal, Martti; Sarkar, Uptal (1999). "Probing the Exotic Particle Content Beyond the Standard Model". European Physical Journal C 8 (2): 301. arXiv:hep-ph/9808484. Bibcode:1999EPJC....8..301M. doi:10.1007/s100529901068.