Why is the notation startfraction dy over dx endfraction used to represent the derivative?

We know expression is used for represent the derivative.

Actually, derivative is the second name of " Rate of Change".

And if we read , it represents the "Rate of change of y with respect to x".

In simple words, a derivative is the rate of change or slope of a very small portion of a function.

dy represents very small change in y-coordinate and dx  represents very small change in x-coordinate.

Because deriviate is the second name of " a very small rate of change".

We use to represent the derivative.