solution set

Every tuple that satisfies an equation or system — a point, line, plane, or more.

A solution of a linear equation is a tuple $(s_1,\dots,s_n)$ that makes the equation true when substituted in. The solution set is the collection of every such tuple. Its size depends on $n$ : one variable pins down a single point, two variables generically trace a whole line, three a whole plane; beyond three there's no picture, but the solution set of a linear equation in $n$ variables is called a hyperplane in $\mathbb R^n$ .