The meaning of thermonuclear fusion is, thermonuclear fusion is a nuclear reaction in which 2 light atomic nuclei combine to form a heavier nucleus, which releases a tremendous amount of energy.
The process of thermonuclear fusion often requires extremely high temperatures and often in the millions of degrees F and Celsius in order to overcome the electrostatic repulsion that occurs between the positively charged nuclei.
The Sun as well as other stars are also powered by thermonuclear fusion.
The process of thermonuclear fusion involves extremely high temperatures, plasma state, fusion process and energy release.
The extremely high temperatures provide the nuclei with the needed sufficient kinetic energy to be able to collide with enough force to fuse together.
At these extremely high temperatures, the matter exists as plasma, which is a state where the atoms are stripped of their electrons, which creates a mix of free ions and electrons.
And when the nuclei get close enough, the strong nuclear force then overcomes the electrostatic repulsion which causes them to fuse.
This fusion then results in a more stable nucleus with a slightly lower mass than the original nuclei.
And the missing mass is then converted into a large amount of energy, which is also described by Einstein's famous equation of E=mc2.
The most common fusion reactions involve isotopes of hydrogen such as deuterium and tritium, which fuse to form helium.
And thermonuclear fusion is also the power source of stars and is also being researched for potentially being used in fusion power plants to offer a clean and potentially limitless source of energy.