- It is a quantity that is not expressible in terms of any other quantity of a different kind but it can be expressed in terms of its own units only.

- Fundamental units are arbitrarily selected and cannot be derived from other units.

- Units of base quantities are termed "fundamental units" and they form a complete set of units.

Derived quantity:

- It is a quantity that can be expressed in terms of two or more fundamental quantities.

- They can be derived from combinations of fundamental quantities.

Some examples of fundamental and derived quantities are given:

Fundamental quantities:

- Mass (kg)

- Length (m)

- Time (s)

- Temperature (K)

- Electric current (A)

- Luminous intensity (cd)

- Amount of substance (mol)

Derived quantities:

- Speed (m/s)

- Density (kg/m3)

- Area (m2)

- Volume (m3)

- Force (kg m/s2)

- Energy (kg m2/s2)

- Power (kg m2/s3)