1 : the act of giving something in return for something received
2 : the key on the typewriter keyboard that shifts from lower-case letters to upper-case letters
3 : the act of reversing the order or place of
4 : reciprocal transfer of equivalent sums of money (especially the currencies of different countries)
5 : an equal exchange
6 : income (at invoice values) received for goods and services over some given period of time