An Expression Tree is a binary tree used to represent mathematical expressions. Each leaf node contains an operand, such as a number or variable, while each internal node represents an operator, like addition, subtraction, multiplication, or division. This structure allows for easy manipulation and evaluation of expressions. Expression trees are particularly useful in compilers and interpreters for programming languages, as they facilitate the parsing and evaluation of complex expressions. By traversing the tree, one can compute the result of the expression or convert it into different forms, such as prefix or postfix notation.