Question

what called unit and fundamental unit ?

Answer 1

A fundamental unit a unit of measurement for a measurable physical property from which every other unit for that quantity can be derived.
The fundamental unit for a particular measurable quantity is chosen by convention.

They are the units of the fundamental dimensions of physics.

Answer 2

Fundamental units are the units which are not dependent with any other units like length, mass, time, electric current, thermodynamic temperature, amount of substance, or luminous intensity in the International System of Units, consisting respectively of the meter, kilogram, second, ampere, kelvin, mole etc