mole

https://doi.org/10.1351/goldbook.M03980
The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 x 10E23 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol-1 and is called the Avogadro number.
The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.
Note:
The formulation of this definition was agreed upon by the 26th CGPM in November 2018 with effect from 20 May 2019.
Source:
BIPM, The International System of Units, SI Brochure, 9th ed. (2019) (http://www.bipm.org/en/publications/si-brochure/)