A monomial is an expression with one term (ex: x, 5y, 6z, 8wxy, b²)
A binomial is an expression with two terms (ex: 4 - 6y, 5x + 2z, 3w + 7, xyz + abc)
A trinomial has three terms
A constant is a term with no variables - a number, in other words, like 3, 4, 154, 78, etc.
The expression 12xyz - 45 has two terms, 12xyz and 45, making it a binomial.