I'm a high school maths teacher.
I was wondering if there is a name for all equations where a variable appears only once e.g.
$$\frac{(x+3)^2}{4}=5\qquad {\rm{or}} \qquad \frac{1}{2}+x=\frac{3}{4}$$
I was planning on introducing the "onion method" for solving to my students and lots of them like knowing the names of equations.
Informally, I would call these arithmetic equations since arithmetic is all that's required to solve them.
Thanks, Ben