A number or symbol, often written as a subscript or superscript to a mathematical expression, that indicates an operation to be performed on, an ordering relation involving, or a use of the associated expression.

• 指数，根指数一个数或符号，多写于数学表达式的下部或上部，表示一个有待完成的计算，或相应的次序关系，或一个相关表达的运用