What is proton.

Proton.
Elementary particle in the nucleus of all atoms, elementary particle with a positive electrical charge.

Otherwise:
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number. The name proton was given to the hydrogen nucleus by Ernest Rutherford in 1920, because in previous years he had discovered that the hydrogen nucleus (known to be the lightest nucleus) could be extracted from the nuclei of nitrogen, and was thus a candidate to be a fundamental particle and building block of all complex atomic nuclei.