Question: I want to ask what is the little numbers on top/over any random number? For example, 75 in² and 125 ft3. What is it called and what does it mean is my question. I couldn't find anything online since I don't know what it is called.

Answer: 
The general term for a number (or other text) written like this is **[superscript](https://en.wikipedia.org/wiki/Subscript_and_superscript)**.

The term in2 refers to [square inches](https://en.wikipedia.org/wiki/Square_inch), which is the amount of area in a square with sides an inch in length.

Likewise, if it were in3, it would be referring to [cubic inches](https://en.wikipedia.org/wiki/Cubic_inch), which is the amount of volume in a cube with side lengths of an inch.
**Exponent** 

> 
> 3.6 Derived Units— Derived units are formed by combining base units according to the algebraic relations linking
>  the corresponding quantities. Symbols for derived units are obtained by means of mathematical signs for
>  multiplication, division, and the use of **exponents**. For example, the SI unit for speed is the meter per second
>  (m/s or m·s–1 and that for density is kilogram per cubic meter kg/m3
>  or kg·m–3). Most derived units have only
>  their composite names, such as meter per second for speed or velocity. Others have special names, such as
>  newton (N), joule (J), watt (W), and pascal (Pa), given to SI units of force, energy, power, and pressure (or
>  stress), respectively. 
> 
> 
> 

SAE Technical Standards Board: Rules for SAE Use of SI (Metric) Units, Rev May 1999.
<https://www.sae.org/standardsdev/tsb/tsb003.pdf>