Quantity is an attribute, which is represented by amplitude and repetition times. It is the basic category of things like quality, essence, change and relationship. The concept of quantity begins with share, that is, an entity that can carry quantity. As a basic vocabulary, quantity refers to any quantitative attribute or characteristic of things. Some quantities are determined by their properties (such as numbers), and some quantities are used as descriptions of states (attributes, dimensions and characteristics), such as weight and lightness, length and short, width and narrow, big and small, and more and less.

The quantity belonging to the second degree is discrete and can be decomposed into inseparable units, such as collective nouns: army, fleet, sheep, government, company, party, crowd, choir and number. The amplitude is continuous and can be decomposed all the time, including all non-collective noun: universe, matter, energy, liquid and matter.

The physical quantity of various extended data has its unit of measurement, and the number of selected substances displayed under specified conditions is taken as the standard of basic unit of measurement. Why are the basic quantities chosen by different disciplines different in different periods?

For example, in physics, seven physical units, such as time, length, mass, temperature, current intensity, luminous intensity and quantity of matter, are taken as basic quantities, and their units are seconds, meters, kilograms, kelvin, amperes, Candeira and moles.

References:

Baidu Encyclopedia-Quantity