Infix Expression
Whenever operator is between the operands, then the expression is called infix expression.
Suffix Expression
Whenever the operator is on right side of the operands then the expression is called suffix or postfix or reverse polish expression.
Prefix Expression
Whenever the operator is on left side of the operand then the expression is called prefix or polish expression.
Fully Parenthesized Expression
A pair of parentheses has the same parenthetical level as that of the operator to which it corresponds, i.e., of the operator, which is immediately enclosed by this pair. Such an expression is called a fully parenthesized expression.
Parenthetical Level
Starting from the innermost parenthesis to the outermost parenthesis, we solve the expression based on the level of parenthesis is called the parenthetical level. [Innermost parenthesis have the highest priority].