Solution: ① Coefficient in algebraic expression: refers to the specific number before the unknown (including the symbol before it).

② Number of terms in algebraic expression: See how many plus or minus signs this polynomial has, and the number of terms is always one more than the number of plus and minus signs.

③ Degree: In a polynomial, find out the degree of this algebraic expression with the largest exponent in each term.

④ Merging similar terms: If there are two or more monomials with the same letter and index, we can merge them, that is, find the algebraic sum of their coefficients.