In pure math, equations aren't often named. For instance, we might define that $f$ is a (real) polynomial function iff there exists a finite sequence of real numbers $a_i$ such that $$f(x)=a_0 + a_1 x + \cdots a_n x^n.$$
Notice, though, that we haven't defined an equation, but rather a kind of function.
Furthermore, we might define that a solution multiset of a polynomial function $f$ is a multiset of real numbers $x$ such that $f(x)=0$, with the additional requirement that the multiplicities are correct. Again, note that we've defined a way of getting a multiset from a function; technically, this is another function! Its certainly not an equation.
However, in applied math, I've noticed a lot more naming of equations / syntactical objects. Like, a text might define that a polynomial equation is an equation of the form $$a_0 + a_1 x + \cdots a_n x^n = 0.$$
Why is this the case?