There do seem to be a number of these questions - linear ones come under various headings, but there are quadratic and cubic ones around. I wanted to retag a post with simultaneous-equations, and discovered it wasn't there. Any views on whether this tag would be useful?
This is just to post a counterargument to that advanced by user pau2357paul:
I think the attempt to compare with the [algebra] tag is a false analogy. A better tag to compare to would be the convergence tag, which describes a general concept but which has different manifestations in introductory real analysis, general topology, functional analysis, and so forth. Another similar tag is continuity.
Note that each question is allowed to have five tags. It would be reasonable to read the tag combinations
(simultaneous-equations) (pde)to mean simultaneous partial differential equations
(simultaneous-equations) (differential-equations)to mean simultaneous ODEs
(simultaneous-equations) (linear-algebra)to mean simultaneous linear algebraic equations
(simultaneous-equations) (analytic-geomety)to mean simultaneous equations arising from a geometric context
(simultaneous-equations) (polynomials)for the case of solving nonlinear, algebraic equations
Also, as an aside, I would personally prefer
(simultaneous-equations), but that is just an irrational personal preference and I won't make too big a deal of it.
I'd prefer to keep the discussion about system of equations in one place (and I don't think this will generate enough discussion to deserve a separate question). So I'll point out here that there exists a tag called nonlinear-system. (I only noticed it now.)
What should we do with this tag. Should it by made synonym of the newly created systems-of-equations?
If we keep the two tags separate, the usage of nonlinear-system should be clarified. (Tag-wiki and tag-excerpt are empty at the moment.)
It is a good idea of having the specific tags for simultaneous-type equations, as questions about simultaneous-type equations are often more advanced than that of non-simultaneous-type equations, but you should note that the term "equations" itself is in fact too vague, as the types of equations contain at least algebraic equations, transcendental equations, diophantine equations, ordinary differential equations, partial differential equations, difference equations, integral equations, and any composite types of them as http://en.wikipedia.org/wiki/Equation#Types_of_equations classified, so as the simultaneous-type equations.
It is lucky that in MSE nobody has created the equations tag so that the arguments like The use of the [algebra] tag not appeared in the equation-types tags. If you create the simultaneous-equations tag, the arguments like The use of the [algebra] tag will appear again, the tag names about equations will become inequality and eventually brings the inappropriate culture of tagging. So if you want to create the specific tags for simultaneous-type equations, please create the tags like simultaneous-algebraic-equations, simultaneous-transcendental-equations, simultaneous-ordinary-differential-equations, simultaneous-partial-differential-equations etc.