Which is an example of an algebra expression

Examples:

3xy and - 5xy are like terms (same variables).

3xy and - 5xym are not like terms (the second term has a variable that the first doesn't).

-2m2xh and 4m2hx are like terms (same variables and exponents, just in different order).

-2m3xh and 4m2xh are not like terms (the variable m has different exponents in each term).

If there's more than one term separated by plus or minus signs, then we have an expression. For example:

5x2y - 3xy + y + 5

This expression has four terms: 5x2y, - 3xy, y (or 1y), and 5.

2x+20=100 ...