TITLE: Total Derivatives and Total Differential
QUESTION [5 upvotes]: I am confused between total derivatives and total differential. What is  the difference between total derivatives and 
total differential?

REPLY [3 votes]: the total differential is 
$dz = \frac {\partial z}{\partial x} dx + \frac {\partial z}{\partial y} dy$
How much do we expect $z$ to change for some changes in $x$ and $y?$
The total derivative is 
$\frac {dz}{dt} = \frac {\partial z}{\partial x} \frac {dx}{dt} + \frac {\partial z}{\partial y} \frac {dy}{dt}$
$x,y$ are both functions with respect to parameter $t$
what is the derivative of $z$ with respect to this parameter?