An equation with two or more variables is called a polynomial. It can also be a literal equation.
A numerical expression is an equation that contains only numbers. An algebraic expression is an equation that contains one or more variables and can also have numbers.
An open sentence is an equation that contains one or more variables and letters for the opening to fill in the spaces.
well, an equation with one variable is a one step equation and an equation with more than 2 variables is a multi-step equation
It is called a polynomial.
a+b=16 is a linear equation in two variables. The variables are a and b. To solve a linear equation in 2 variables we need more information. We need either another equation, or a value to put in for a or b.Since we have neither, there is no more we can do.
The solution to an inequality generally is a region with one more dimension. If the inequality/equation is of the form x < a or x = a then the solution to the inequality is the 1 dimensional line segment while the solution to the equality is a point which has no dimensions. If the inequality/equation is in 2 dimensions, the solution to the inequality is an area whereas the solution to the equality is a 1-d line or curve. And so on, in higher dimensional spaces.