The following is a single term:
Here we see the two separate quantities 3 and multiplied by one another. We can also dissect the expression a little further we get 3•x•x•x•x•x•x•x. Notice how all numbers and variables are combined through multiplication only. We say that the above example represents a single term.
When dealing with algebraic expressions the number of different terms that are added to or subtracted from one another give the expression a different name. Here we will look at different types of expressions based on the number of unique terms they contain.
The simplest algebraic expression is just a number, such as 3. A single number is called a constant, or a term that is not multiplied by a variable.
A single algebraic expressions with no other terms added to or being subtracted from it is called a monomial. For example, is a monomial.
Typically when writing algebraic expressions we refer to them using their variable and the power the variable is being raised to. For example, would be called a second degree monomial because it the variable is being raised to the second power.
More complex types of algebraic expression contains more than one monomial and are combined through either addition or subtraction.
If we have two monomials combined with one another we call that expression a binomial. For example, and are binomials.
If we have more than two monomials combined with one another we have what is called a polynomial. For example, is a polynomial. We typically say that this expression is a second degree polynomial because the highest power of any variable in the expression is 2. If we had the expression , we would count the total number of powers in each monomial to determine the power. In this example we would say that this is a 3rd degree polynomial because in the term the combined power of x and y add up to 3.
When working with algebraic expressions you should be familiar with the parts that make up the expression. Here we will discuss and identify coefficients, variables, powers or degree, and constant terms.
If we have the expression , the variable represents an unknown quantity, and is typically written as a letter. In this case the variable would be x. Coefficients would be the number in front of a variables. In this case the 5 and 7 would be coefficients. The power or degree of this polynomial is 2 since that is the highest power variables are being raised to. Finally, the constant would be 3 since that is the only term without a variable component.
Now let’s look at how to combine two or more algebraic expressions.
One way we can simplify expressions is to combine liketerms. Liketerms are terms where the variables match exactly (exponents included). Examples of liketerms would be 3xy and −7xy or and or −3 and 5. If we have liketerms we are allowed to add (or subtract) the numbers in front of the variables, then keep the variables the same. This is shown in the following examples.

Combine like terms  

Combine like terms  

Combine like terms  

Our Solution  
 

Combine like terms  

Combine like terms  

Our Solution 
As we combine liketerms, we need to interpret subtraction signs as part of the following term. This means if we see a subtraction sign, we treat the following term like a negative term, the sign always stays with the term.
Source: Adapted from "Beginning and Intermediate Algebra" by Tyler Wallace, an open source textbook available at: http://wallace.ccfaculty.org/book/book.html