The document is a summary of key concepts in algebraic expressions including:
1) The definition of algebraic expressions as combinations of letters, numbers, and operation signs where letters represent unknown quantities.
2) Examples of monomials, binomials, and trinomials as expressions with 1, 2, or 3 terms.
3) Procedures for adding, subtracting, multiplying, and dividing algebraic expressions including monomials and polynomials.
4) Notable products which can be written directly without calculating the multiplication such as the difference of squares and sum of cubes formulas.