‘Anti’ means the opposite. So anti-matter has some properties opposite with respect to the usual matter.
For example, the electron has as its antiparticle the antielectron. The electron and the antielectron have exactly the same masses, but they have exactly opposite electrical charges.
It is hypothesized that every elementary particle in the Universe has a partner particle, known as an ‘antiparticle’.
The particle and its antiparticle share many similar characteristics, but many other properties are the exact opposite.
The electron, for example, has as its antiparticle the antielectron. They both have the same masses, but they have exactly opposite electrical charges.
Most of the human understanding of anti-matter comes from high-energy accelerator experiments.
When a matter particle meets its antimatter particle, they destroy each other completely (i.e. annihilation), releasing the energy equivalent of their rest masses (following Einstein’s E = mc2).
For instance, when an electron meets an antielectron, the two annihilate and produce a burst of light which produces a corresponding energy level equivalent to the masses of the two particles.
Negative Matter and Negative Energy
Negative matter is a hypothetical type of matter which if it exists will have negative mass and negative energy.
It will in essence have a negative gravitational charge and repel normal matter. Yet it will interact just like any other matter in every other way.
Hope you remember that matter and anti-matter will attract each other resulting in annihilation. But matter and the negative matter will repel each other under gravity.
Neutrinos
Proton, neutron, and electron are tiny particles that make up atoms. The neutrino is also a tiny elementary particle, but it is not part of the atom.
A neutrino is a subatomic particle that is very similar to an electron but has no electrical charge and a very small mass, which might even be zero.
There are actually three kinds of neutrinos: the electron neutrino, the muon neutrino, and the tau neutrino.