No, it's an equation. Equation is a statement that says that thing A is equal with thing B. The point is that thing A and thing B are often quite dissimilar in form. But since they are the same thing, and because math is deterministic, if you manipulate the both sides the same way (For example, multiply both sides with the same amount), it stays equal. (Plus sometimes you are allowed to manipulate them in different ways, because the axiomatic system you're in says that's allowed for some cases. Example: you are allowed to rewrite (AB)C as A(BC) if you know that the object you are manipulating is associative.) "Solving" an equation means manipulating it in a way that the other side becomes trivial in form. You maybe can't do that for many differential equations, but that doesn't make them less of equations.