A proton is the positively charged subatomic particle located inside a nucleus.
Protons are important because it is their number that determines the element (of which the atom is part) and its chemical properties.
To put it simply, the number of protons in an atom, or the atomic number, defines the type of an atom. Thus an oxygen atom differs from a helium atom on the basis of its atomic number. That number is denoted by the letter ‘Z’.
The word ‘proton’ was derived from a Greek word meaning ‘first’. It was named by Ernest Rutherford in 1920. One or more protons are present in every nucleus. Together, protons and neutrons form what is known as nucleons.
Further, protons are made up of invisible particles called ‘quarks’. There is a strong nuclear force that binds these quarks with each other. It is also the same force that primarily contributes to the mass of the proton, rather than the quarks themselves.