Question 559096
You are right. {{{4a^2b^5}}} is a monomial.
Some may also call it a polynomial, just as the empty set is called a set, and how a square is considered a special case of a rectangle.
{{{4a^2b^5+2}}} would be a binomial. Each group of multiplied numbers and variables (with any exponents) between plus and minus signs is called a term and if you count two terms, it is a binomial. Three terms makes a trinomial, and if you don't want to count, you call it a polynomial.