The word Antimatter was first coined by Arthur Schuster in 1898.He hypothesized anti atoms, as well as whole antimatter solar systems, and discussed the possibility of matter and antimatter annihilating each other. These were not serious theories, merely speculation and widely differed from the modern concept of antimatter in that it possessed negative gravity.
The modern theory of antimatter started in 1928, with a paper by Paul Dirac. He realized that his realistic version of the Schrödinger wave equation for electrons predicted the possibility of anti electrons.
In particle physics, Antimatter is defined as a material consisting of antiparticles, which have the same mass as particles of ordinary matter but have opposite charge and other particle properties such as lepton and baryon number. Interactions between particles and antiparticles lead to the annihilation of both, giving rise to varying proportions of high-energy photons (gamma rays), neutrinos, and lower-mass particle–antiparticle pairs. Putting aside the mass of any product neutrinos, which represent released energy which generally continues to be unavailable, the end result of annihilation is a release of energy which is proportional to the total matter and antimatter mass, in accord with the mass-energy equivalence equation by Albert Einstein i.e. E=mc2
Antiparticles combine with each other to form antimatter just as ordinary particles combine to form normal matter.
Antimatter is generally produced in two forms
1.) Antimatter in the form of anti-atoms is one of the most difficult materials to produce.
2.) Antimatter in the form of individual anti-particles, this is however commonly produced by particle accelerators and in some types of radioactive decay.
Example, a positron (the anti particle of an electron) and an antiproton can form an anti hydrogen atom. Physical principles indicate that complex antimatter atomic nuclei are possible, as well as anti-atoms corresponding to the known chemical elements. To date, however, anti-atoms more complex than anti helium have neither been artificially produced nor observed in nature. Studies of cosmic rays have identified both positrons and antiprotons, presumably produced by high-energy collisions between particles of ordinary matter.