What is mass, really? We all know that mass is the cause of the force of gravity. If there is no mass, then there will be no gravity force. One cannot exist without the other. According to Newton, gravity is an attractive force. For Einstein, gravity is the curvature of spacetime continuum. But gravity by any other names is still just gravity. In almost every case, changing name of a concept does not completely clarify the true nature of the concept. Newton defined mass as the product of density and volume. But he initially defined density as the ratio of mass over volume. This is a good example of definition by milder circumlocution, which amount to no definition at all but a postulated assumption for the benefit of validating a physical concept. Einstein made the formulation that mass is equivalent to energy in his theory of special relativity. What he really meant is that rest mass is equivalent to energy. But which energy is he talking about? There are two known energy concepts accepted before 1905. These are the kinetic and the potential. Kinetic energy is energy of motion. For it to exist, there must be motion. What is in motion? Answer is motion of mass. We are back to mass. What is mass? Why does it move? Why does it have to stay motionless for it to be equivalent to energy? But when mass moves, its magnitude increases. But does its rest-mass energy decrease? No, the kinetic energy increases. But kinetic energy is not the rest-mass energy mentioned above. The rest-mass energy must be the potential energy, which is energy of position in an abstract field of force. In this case, it is the force field of gravity. All force fields in nature are conservative. They have a center. The force increases in motion toward the center and decreases in motion away from the center. There are two known physical fields. These are the scalar field and the vector fields. Concepts like temperature, density and energy are all scalar fields. Examples of vector fields are the electric field, the magnetic field, the gravitational field, the weak nuclear field and the strong nuclear field. But what is the field for mass? This is agreed to be the Higgs field, which is a scalar field. It has positional magnitude but spherically symmetrical and hence gives no preferred direction in any abstract space. But how can something of no-force origin gives force to all other forces? The answer is perfect symmetry (not the book by Heinz R. Pagels). This perfect symmetry belongs to the pure vacuum of zero-dimension. Pure or perfect vacuum of zero-dimension has an infinite of points with no detectable motion (absolute or relative). This is an assumption. It cannot be proved nor disproved by performing any kind of physical experiment. But we can also made one more assumption for this pure vacuum. But once one, of these infinite 0-dim points, moves in a chosen direction, this chosen direction is kept for all eternity. This is the principle of a directional invariance. This principle, at the least, gives a new definition of quantized space and hence gives two definitions for mass: the potential and the kinetic. The fermions are the potential mass. The bosons are the kinetic mass. The mathematics for the principle of directional invariance is the use of Hadamard’s matrices when they are taken as perfectly symmetrical by not containing any zero. The elements of these matrices are either 1 or –1. These can be arranged in an infinite ways. The matrix addition operation gives charges from space charges to color charges to electric charges. The matrix multiplication operation gives the diverse experimental masses of the elementary particles. This operation also shows that photon has zero potential mass but non-zero kinetic mass. The neutrino does have potential mass but very small to the point of being undetectable. That the antiparticles of nature are all moving in the other direction of time, while particles of matter are moving in the same direction of time as the entropy of thermodynamics. Contrary to accepted notions, stars are made out of a thermodynamic equilibrium between potential mass and kinetic mass. Their longevities can be attributed to the effect of this equilibrium. The formations of Cooper pairs in superconductivity are just the effects of potential mass trying to reach the energy state of kinetic mass. If this equilibrium can be fully understood, then all these promising technologies of thermonuclear fusion and high temperature superconductivity can all be realized.