Dx Rx Heart Failure

Okay this may sound stupid but I need a little help. Furthermore, I understand the meaning of $\frac {dy} {dx}$ and $\int f (x)dx$, but outside of that what do $dy, du, dx$ etc. Moreover, This doesn't make sense. In related context, These identities for dx d x and dx d x are sometimes called the "sophomore's dream". These findings regarding Dx Rx Heart Failure provide comprehensive context for understanding this subject.