I teach secondary and postsecondary math courses. The term "literal equation" was used in Texas where I taught for 17 years. The Algebra 1 state standard A.12E says that students are expected to "solve mathematic and scientific formulas, and other literal equations, for a specified variable." I also taught college undergrad courses in Texas, including College Algebra, and I don't recall ever seeing the the term used there, but I used it in class because my students were familiar with it. Now I teach in Oregon, and the term is not a part of this state's standards from what I can tell.

Maybe it's not universal but in school literal equation basically meant there were letters instead of numbers.

It's the term we use for instance when going from the equation of a line like y=3x+2 to lines in general y=ax+b (a and b in ℝ)

And i agree it's a lot better to specify to solve for x (because you can solve for anything or have multiple variables).

Although x being a variable, and solving for it would be the most logical assumption.