The gift tax is imposed on the "transfer of property by gift." The term gift is not expressly defined either in the Code or in the Treasury Regulations. However, section 2512(b), dealing with the valuation of gifts, states that "where property is transferred for less than an adequate and full consideration in money or money's worth," the difference between the value of the property transferred and the consideration received constitutes a gift. Thus, for gift tax purposes, the determination of whether a gift was made does not turn so much on the intent of the transferor as it does on the mechanics of the transfer whether property was transferred without full and adequate consideration in money and money's worth. The absence of donative intent still can be a significant factor.
Kahn, Douglas A. "Transactions Subject to Gift Tax." E. M. Colson, co-author. Prac. Law. 21 (1975): 81-93.