Quote by Sorry!
Curly d is used for partial derivatives. Regular d is for a total derivative.
Partial derivatives are when treat one variable as a variable and keep the rest as constants ignoring the relationship between the variables.
Total derivatives are when you do the same as above but the relationship between variables remains.

Thanks, i did remember the curly d being used alot in partial deriv's, but wasnt sure that was their sole use. Thanks for clearing it up