# What's the meaning of a "d" with a stroke when using Leibniz notation?

by Carlos Gruss   Last Updated August 13, 2019 20:20 PM

I'm studying engineering and there's a physics teacher that strikethroughs the derivative $$d$$ when writing an expression for power (which is work over time). I know physics teachers are known to abuse mathematical notation, but this intrigued me as I had never seen it used and couldn't find anything online. So the expression she writes is:

$$đW/dt = ...$$

What does it mean for the $$d$$ to be struck like this?

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I've seen this frequently in physical chemistry books. It's to remind you that this is an inexact differential that results in a path-dependent integral. So, for example, it would be used with $$dq$$ or $$dw$$, but not with $$dE$$ or $$dS$$. They call $$E$$ and $$S$$ state variables, but $$q$$ and $$w$$ are really not well-defined functions — they depend on the path/process, not just on the endpoints.