Parts of an Algebraic Expression ... Revision

One of the most important ideas to understand in algebra is the vocabulary associated with it.You will encounter words such as 'variable', 'terms', 'coefficient' and  'constant'. These are all words used to describe an algebraic expression.
First of all, what is an expression? An expression is a number sentence without an equal sign.
An algebraic expression is an expression containing variables, number and operation symbols.
Example i: 5a - 8b + 6
Example ii:  yz - 3z + 7y - 4
The parts of an algebraic expression that are added together are called terms. In the algebraic expression 5a - 8b + 6, the terms are '5a', '-8b' and '6'. A term can be a constant, a variable, or a constant multiplied by a variable or variables.
So, what on earth is a variable? A variable is a letter used to represent one or more numbers. In example i above, the variables are 'a' and 'b'.
A constant is a term that has no variable part. It is a number that stands by itself such as '6' in example i and '-4' in example ii.
When a constant is multiplied by a variable or variables, that constant is called a coefficient. So '5' in the term '5a' is a coefficient.