Definition:Mole

Mole
The mole is the SI base unit of amount of substance.

It is defined as exactly Avogadro's number of particles, that is, $6 \cdotp 02214 076 \times 10^{23}$. The specific type of particle under discussion must be specified.

They are usually the elementary units of a particular substance under discussion.

However, as long as the particles are more-or-less identical, there is no specific limitation to what a mole may be applied to.

A beloved teacher of chemistry at a certain editor's school, when covering the subject, would habitually spend some time discussing a mole of cricket balls.