In the most ELI5 way possible, a superconductor is a material that doesn't lose any energy or produce heat when used as a cable/wire, and at the same time also a very strong magnet.

MRIs and powerlines are more obvious applications, but theoretically you can do a lot of cool stuff (batteries with zero energy loss, heat-efficient computers, etc [1]). If true, LK-99 would allow these things to happen at room temperature instead of negative whatever degrees, making them much more useful.

[1] https://en.m.wikipedia.org/wiki/Technological_applications_o...