(1) An algebraic expression consisting of the product of numbers or letters is called a monomial, and a single number or letter is also called a monomial.

(2) Polynomial An algebraic expression consisting of several monomials is called a polynomial.

③ Coefficient: The sum of the indices of all letters in a monomial is called its number.

④ Times: The sum of the indexes of all variables in a single item is called the times of this single item.

⑤ Term: Each monomial that constitutes a polynomial is called a polynomial term.

⑥ Degree of Polynomial: The degree of the term with the highest degree in a polynomial is called the degree of the polynomial.

⑦ Similar terms: In polynomials, terms with the same letters and the same index of the same letters are called similar terms.

⑧ Merging similar terms: Merging similar terms in polynomials into one term is called merging similar terms.