If you've searched the topic "equation vs. expression" on the net & found this page, you will probably read the following four items as mostly the same.

1. Ten is five less than a number.
2. A number is less than five.
3. a number less than five
4. five less than a number

      Please now reconsider the above items and determine which are sentences (subject, verb, complete idea) and which are phrases (no subject, no verb). For assistance from an English point of view, see http://www.richmond.edu/~writing/wweb/fragment.html

      The mathematical term expression is equivalent to an English phrase. The most common mathematical statements or sentences, are called equations and inequalities. The reader is asked to review each of the links in this paragraph before reading further and to pay particular attention to the mathematical terms relation and relation symbol, the "verbs of mathematical statements," as they relate to each of the other words.

      The algebra student, or algebraically able individual, is expected to know the difference between an expression and a statement because each serves a different purpose and each is handled in a certain way.