In the realm of particle physics, supersymmetry is actually a respectable concept.
Remember that we have two classes of particles, namely fermions and bosons. Particles that comprise matter such as electrons and quarks, are fermions - they have half-integer values for the spin quantum number, and obey what are known as Fermi-Dirac statistics. This means that within in well-defined quantum system, no two fermions can share the exact same values for their quantum numbers, and this explains why electrons are arranged in shells in atoms.
Bosons, on the other hand, are particles with integer values for the spin quantum number, and are associated with forces of nature - the photon, the Higgs Boson, the W and Z bosons etc. These particles obey what are known as Bose-Einstein statistics, and multiple bosons in a well-defined quantum system can share the same values of their quantum numbers.
As an aside, it’s worth pointing out a correlation between the spin quantum number of bosons, and the nature of the forces they underpin. The Higgs Boson is associated with mass, which is a scalar physical quantity, and has spin 0. The photon, W and Z bosons all have spin 1, and are associated with vector forces - electromagnetism and the weak nuclear force. The hypothetical graviton, yet to be found but considered to be associated with gravity, has spin 2, and this is because the Einstein field equations reveal that gravity is properly a tensor force.
Indeed, in the mathematical realm of tensor, the rank of a tensor is directly related to the nature of the physical quantity being represented by that tensor. A scalar quantity is a rank 0 tensor, a vector quantity is a rank 1 tensor, and so on. The spin quantum number of a boson is therefore an indicator of the nature of the force that said boson underpins.
That diversion about bosons above aside, it’s now time to reveal the basis of supersymmetry. The observed division into fermions and bosons is considered to be the result of symmetry breaking as ambient energy density decreased after the Big Bang, just as the appearance of W and Z bosons as observably separate underpinnings of the weak nuclear force is considered to be the result of symmetry breaking of a different sort, as ambient energy density decreased. Ramp up the energy density in a particle accelerator, and the photon joins up with the W and Z bosons to underpin a unified electroweak force.
So, what happens if you ramp up the energy density still further? Sypersymmetry theory predicts that the result will be the emergence of new, partner particles to the existing ones. The currently known bosons will have fermion partners - labelled photinos, winos, zinos and higgsinos (the -ino suffix denotes these fermionic superpartners, as they’re called). Likewise, fermions will have boson partners - the selectron and squarks (these superpartners denoted by the s- prefix).
However, there’s a teensy problem with the idea of supersymmetry. Namely, we’re not able to subject it to direct experimental test at the moment.
The reason for this is that the energy density required for the supersymmetric partners, if they exist, to appear, is way beyond what our particle accelerators can reach. By, if memory serves, a factor of about 1015. A particle accelerator capable of generating that sort of energy density would have a diameter greater than the orbit of Saturn, and we’re not in a position even to build one that size, let alone operate it at full capacity.
Consequently, supersymmetry remains an interesting idea, that’s mathematically consistent with known particle physics, but separated from our ability to test it experimentally by a yawning chasm. It’s akin to string theory in this respect, which would require us to achieve even greater energy densities in a particle accelerator to test directly - at this point, we’re considering trying to build a particle accelerator that’s about a light year in diameter in order to reach that energy density.
Unless we can find another means of generating the requisite energy density that doesn’t involve building outlandishly huge machines, both supersymmetry and string theory will remain theoretical.