I have only taken one calculus course in my life so please bear with me. I came across this equation in a paper:
dt = dz/u + d[f(y)]
It looks like Leibniz-notation, but taken apart. My friend told me it's called "differential form". However, it doesn't make sense to me that dt would be something in and of itself. Same goes for dz. An actual infinitesimal difference doesn't really exist, right? Could anyone explain to me what an equation like this is supposed to mean or signify?
Edit: I don't necessarily want a formal definition. Just an intuitive understanding.
Edit 2:
