In order to better represent what does the word "anti", let's take a sheet of paper and write on it some phrase. Then give her to the mirror. Mirrored letters were written from right to left. The whole world has in the mirror like opposite properties.
We can say that the world seen by us in the mirror, is the anti-world that actually exists. Such specular reflection and antiparticles. This is an elementary particle with opposite properties compared to the proton, neutron, electron and other elementary particles. Thus, the electric charge of the proton is +1, and the antiproton - minus 1.
What causes antiparticles and what is their role in the Universe?
Scientists have found that antiparticles when confronted with their corresponding particles (for example, if the electron will collide with positron) are converted to gamma-radiation.
This process is called annihilation. Anatomy consist of antiprotons, antineutrons and positrons, and those, in turn, form antimatter.
At the birth of our Universe antimatter was of great importance.