mole

The term mole can refer to several distinct concepts in science, espionage, and biology. In science, it denotes a standard unit of amount of substance. In biology, it refers to a small burrowing mammal. In espionage, a mole is a spy or infiltrator.

The mole is the SI base unit for the amount of substance. It is defined as exactly 6.02214076×10^23 elementary entities. The unit links macroscopic quantities with the number of constituent particles, enabling calculation of mass, molecules, or atoms in a sample. It is widely used in chemistry, physics, and related fields. The name derives from Avogadro's number, the approximate number of particles per mole.

Moles are small, fossorial mammals in the family Talpidae. They have cylindrical bodies, velvety fur, minimal external ears, and strong forelimbs with large claws for digging. They typically live underground in tunnels and feed mainly on earthworms and other invertebrates. They occur in temperate regions of the Northern Hemisphere, with various species adapted to different soils and climates. They have reduced eyesight and rely on tactile and chemical senses.

In espionage, a mole is a person who has infiltrated an organization to provide information to an outside party. Moles may operate covertly for extended periods.