What is the opposite to ordinary matter called?

The opposite of ordinary matter is called antimatter. It is made of antiparticles, which correspond to the particles found in ordinary matter but have opposite electric charges and other reversed quantum properties.

For example, the antimatter counterpart of the negatively charged electron is the positively charged positron. When matter and antimatter meet, they can annihilate, converting their mass into energy and often producing photons or other particles.

Antimatter is not purely fictional or confined to laboratories. It can form naturally in cosmic-ray interactions and certain radioactive decays, while particle accelerators can create small quantities. Positrons are also used in positron-emission tomography, or PET scans. A common mix-up is treating antimatter as a negative version of matter: its mass is positive, but its corresponding charges are reversed. The visible universe appears to contain overwhelmingly more matter than antimatter, and explaining that imbalance remains a major question in cosmology.