What is delta in physics?

Delta in physics: The Greek capital letter delta would be the traditional mathematical sign for representing a change as well as variation in some kind of quantity or object. A velocity change would be represented by delta-v or $∆\mathrm{v}$.

Example: If somehow the variable 'x' represents an object's movement, then 'x' represents the change throughout the movement.

Therefore, delta ($∆$) represents the change in the object.