A fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state.

the UK's national laboratory for fusion research.

a joint undertaking of the European Atomic Energy Community (Euratom) that is responsible for the EU's contribution to the International Thermonuclear Experimental Reactor, the world's largest scientific partnership aiming to demonstrate fusion as a viable and sustainable source of energy.