WIMP

WIMP (or weakly interacting massive particle) is a name coined to mean some subatomic particle that constitutes dark matter, i.e., a dark-matter particle. It would be a particle with no more than a slight effect on other particles other than through gravity, including no (or very little) effect on electromagnetic radiation (thus neutral of electric charge) and therefore invisible. It must have sufficient numbers and mass to create the effects that motivate the dark matter concept. WIMPs remain a theory, but experiments (dark matter detectors) are carried out to detect such particles in Earth's vicinity, and particle-physics experimenters watch for new particles that might occupy the role. The other major dark-matter model (largely dismissed) has it consisting of larger objects (such as free-floating planets), for which the term MACHO as been coined.

The terms weakly and massive are sometimes presumed to have specific meanings, though the term WIMP is also often used generically, using those two terms more loosely. Regarding specific meanings, "massive" is sometimes taken to mean the particle has considerable mass, e.g., more then a neutron, and "weakly" is sometimes taken to mean that the particle specifically responds to the weak force. A reason for the interest in this more-specific notion of WIMPs is that models of the decoupling in the early universe suggest that such a particle would remain as a relic totaling (roughly) the same total mass (throughout the universe) as that needed to explain the dark matter concept, a coincidence termed the WIMP miracle. Taking WIMP to have this specific meaning, additional terms have been coined for particles that don't quite fit, such as WISP (weakly interacting slim particle, like a WIMP but with little mass) and GIMP (gravitationally interacting massive particle, that interacts with other particles only through gravity).

Given its less specific usage, a WIMP could be currently-known neutrinos (if new knowledge revealed far more exist than currently determined) or it could be an axion, or some as-yet unknown subatomic particle for which the mass and numbers were sufficient.

Presuming it does respond to the weak force, it could be some unknown type of electrically-neutral lepton (which could be termed an additional type of neutrino: that's merely nomenclature) and these have indeed been hypothesized on the basis of particle physics. Or it could be a supersymmetric particle, for which a theoretical candidate is the most massive of the (hypothesized) neutralinos, which has been a strong candidate, but for considerable time, particle-physics experiments have failed to detect them or any other further physical evidence of supersymmetry.