"It's one of the greatest puzzles in physics. All the particles that make up the matter around us, such electrons and protons, have antimatter versions which are nearly identical, but with mirrored properties such as the opposite electric charge. When an antimatter and a matter particle meet, they annihilate in a flash of energy."
https://phys.org/news/2020-12-discovery-great-mystery-universe-antimatter.html
"Matter is any substance that has a mass and a volume. The matter is made up of atoms. An atom is made up of subatomic particles. However, we usually consider atom as the basic unit of matter. The term matter does not include massless particles such as photons. Moreover, energy phenomena such as light and sound are not considered as matter."
https://www.differencebetween.com/difference-between-matter-and-antimatter/
"According to the Standard Model of particle physics, every known type of particle has an antimatter counterpart (though there’s hardly any trace of antimatter in the universe today)."
https://www.discovermagazine.com/the-sciences/alien-antimatter-crashes-into-earth
"Theoretically, a particle and its antiparticle (for example, a proton and an antiproton) have the same mass but opposite electric charge and other differences in quantum numbers."
https://www.nuclear-power.com/nuclear-power/reactor-physics/atomic-nuclear-physics/fundamental-particles/what-is-antimatter/
"Every physics process we know of creates equal amounts of matter and antimatter."
https://www.sciencefocus.com/space/antimatter-where-did-it-go/
"Antimatter is a material composed of so-called antiparticles. It is believed that every particle we know of has an antimatter companion that is virtually identical to itself, but with the opposite charge"
https://phys.org/news/2016-01-antimatter.html