If the "algebra" tag is declared heretical, as suggested here, then what should one do with algebra questions for which neither the "abstract algebra" tag nor a "precalculus" tag is appropriate?
Other "algebra" tags include linear-algebra (currently 4940 questions with this tag), group-theory (2555), matrices (2200), commutative-algebra (1363), polynomials (1164), ring-theory (998), field-theory (707), vector-spaces (634), representation-theory (590), finite-groups (579), modules (466), galois-theory (389), eigenvalues (361), homological-algebra (254), finite-fields (241), roots (191), abelian-groups (187), eigenvectors (175), determinant (172), numerical-linear-algebra (171), relations (167), boolean-algebra (165), and many, many more.
On math.SE, “abstract algebra” is commonly used as a substitute for one of three things: group-theory, ring-theory, and algebras. Possibly many boolean-algebra question also fall to this sinkhole. More specific tags as polynomials (pertain to algebras) and field-theory (pertains to ring theory) should be used as well, but a question tagged with only abstract-algebra is something abnormal.
The whole “abstract algebra” umbrella (as well as its “algebra-precalculus” counterpart) seemingly originates from classification of educational courses in some countries, allegedly USA.
There is also such concept as universal-algebra, although questions tagged so at math.SE demonstrate significant pollution with not-really-universal things mentioned above.