A derivative is a sub function that derives from a main function.
It describes the rate of change/slope in the main function.
The derivative of a constant is 0 because a constant doesn’t change.
The derivative of a linear function is a constant.
The derivative of the exponential is the exponential itself.
When our function has more then one input/variable we need to specify which function we are using for the derivation. That function for a single input/variable is called the partial derivative of that input/variable.
When combining the partial derivatives to one vector we form what is called the gradient.
Which is the change of slope of maximum steepness using all the partial derivatives.