An algebraic Expressions is an expression formed from any combination of numbers and variables by using the operations of addition, subtraction, multiplication, division, exponentiation (raising to powers), or extraction of roots.
For instance,,, , , , and are algebraic expressions. By an algebraic expression in certain variables, we mean an expression that contains only those variables, and by a constant, we mean an algebraic expression that contains no variables at all. If numbers are substituted for the variables in an algebraic expression, the resulting number is called the value of the expression for these values of the variables.

Example:
            Find the value of  when  and .
Solution:
            Substituting  and , we obtain
            .

            If an algebraic expression consists of parts connected by plus or minus signs, it is called an algebraic sum, and each parts, together with the sign preceding it, is called a term. For instance, in the algebraic sum
            ,
The terms are, , and .

            Any part of a term that is multiplied by the remaining part is called a coefficient of the remaining part. For instance, in the term , the coefficient of  is , whereas the coefficient of  is . A coefficient such as , which involves no variables, is called a numerical coefficient. Terms such as  and , which differ only in their numerical coefficients, are called like terms or similar terms.
            An algebraic expression such as  can be considered an algebraic sum consisting of just one term. Such a one-termed expression is called a monomial. An algebraic sum with two terms is called a binomial, and an algebraic sum with three terms is called a trinomial. For instance, the expression  is a binomial, whereas  is a trinomial. An algebraic sum with two or more terms is called a multinomial.

            A polynomial is an algebraic sum, in which no variables appear in denominators or under radical signs, and all variables that do appear are raised only to positive-integer powers. For instance, the trinomial  is not a polynomial; however, the trinomial  is a polynomial in the variables  and. A term such as , which contains no variables, is called a constant term of the polynomial. The numerical coefficients of the terms in a polynomial are called the coefficients of the polynomial. The coefficients of the polynomial above are , , and .
            The degree of a term in a polynomial is the sum of all the exponents of the variables in the term. In adding exponents, you should regard a variable with no exponent as being a first power. For instance, in the polynomial, the term  has degree , the term  has degree , and the term  has degree . The constant term, if it is zero, is always regarded as having degree .
            The highest degree of all terms that appear with nonzero coefficients in a polynomial is called the degree of the polynomial. For instance, the polynomial considered above has degree . Although the constant monomial  is regarded as a polynomial, this particular polynomial is not assigned a degree.

Example:
            In each case, identify the algebraic expression as a monomial, binomial, trinomial, multinomial, and/or polynomial and specify the variables involved. For any polynomials, gives the degree and coefficients.
(a)             (b)             (c)  
Solution:
            (a) Monomial in  and  (not a polynomial because of the variable in the denominator).
            (b) Binomial in  and , multinomial (not a polynomial because of the negative exponent on).
            (c) Trinomial, multinomial, polynomial in  and  of degree  with coefficients , , and .

A polynomial of degree in a single variable  can be written in general form
                        ,
in which  are the numerical coefficients (although any of the other coefficients can be zero), and  is the constant term.