A proton is a positively charged subatomic particle located in the nucleus of an atom. The number of protons, called the atomic number, defines which element the atom is and balances the negative charge of the electrons in a neutral atom. A proton carries a charge equal in size but opposite in sign to that of an electron.

质子是位于原子核中、带正电荷的亚原子粒子。质子的数目称为原子序数,它决定原子属于哪种元素,并在中性原子中平衡电子的负电荷。质子所带电荷与电子大小相等、符号相反。