Google is oversimplifying. The lawson criterion is defined to be the point where heat production by the plasma equals heat loss. For tokamaks (and other magnetic confinement fusion reactors where the confinement time is very long) reaching the lawson criterion is basically all you need to do to achieve ignition - once the plasma is being heated by fusion reactions faster than it is losing heat, it will very rapidly reach the point where it ignites with no further external input.
For short duration fusion (ICF, Magnetized target, Helion, etc) you can exceed the lawson criterion and thus produce gain, but the plasma may still not be long enough lived for the fusion to actually induce more fusion (which is the actual ignition point).
