electron temperature is the temperature of a 📝plasma's electron population, usually quoted in 📝keV — one of the two temperatures a plasma carries at once.
The near-neighbor to keep distinct is ion temperature. A plasma is two interpenetrating populations — light, fast electrons and heavy ions — and collisions equilibrate each species with itself far faster than they couple the two together, so a single plasma routinely holds different electron and ion temperatures at the same moment. Which population is hotter depends on how the plasma is heated: current-driven ohmic heating warms electrons first, while neutral beams deliver their energy mainly to ions.
Electron temperature matters to 📝fusion devices even though electrons do not fuse. The electrons set how the plasma conducts electricity, how strongly it radiates through bremsstrahlung and synchrotron emission, and how efficiently microwave heating couples in. It is also the plasma temperature physicists measure best: Thomson scattering — firing a laser through the plasma and reading the scattered spectrum — yields point-by-point electron temperature profiles and is the gold-standard diagnostic on machines like the 📝Tokamak, complemented by electron cyclotron emission measurements that track the profile continuously in time.