An expression consists of at least two terms and an operation, such as multiply, divide, add or subtract. It does not have an equals sign. When you add an equals sign to an expression it becomes an equation, and there is obviously a term on both sides.
You need to remember that an algebraic expression combines variables (usually specific letters), constants(real numbers) andalgebraic operations (addition/subtraction, multiplication/division, exponentiation).
A polynomial represents an algebraic expression such that:
2x^2 + 3yz + 5^(1/2)
we use algebra when we dont know what a number is, so we use 'x' or 'y' instead of a number.
An algebraic expression consist of one or more terms and a term is product-quotient 0f any combination of numbers and letters(alphabets/variables).
Example of terms : 4, 4*23, 34/5, x, 4x, 8xy, (6a^2)/5c, x^2*p^3, etc
Example of expressions : x, x+5, -78x^3y+ zc^2, (x+4y)(4a+5c), 5x^3- 34x^2 +45 etc
Algebraic expressions use letters of the alphabet to represent variable numbers like
x + y,
x + 2,
(x + 1)(x +2)