Delta (capital δ, lowercase δ) is the fourth Greek letter.

Capital δ is used for:

In mathematics and science, indicating the change of variables.

Any δ particle in particle physics

Lowercase δ:

In mathematics and science, indicating the change of variables.

Names of two functions in mathematics:

Cronecker δ function

dirac delta function

In proofreading, delete the mark.

Square of x square of x

Cube of x cube of x