Child.
Child. For purposes of sections 151(e), 152, and the regulations thereunder, the term child means a son, stepson, daughter, stepdaughter, adopted son, adopted daughter, or for taxable years beginning after December 31, 1958, a child who is a member of an individual's household if the child was placed with the individual by an authorized placement agency for legal adoption pursuant to a formal application filed by the individual with the agency (see paragraph (c)(2) of 1.1522), or, for taxable years beginning after December 31, 1969, a foster child (if such foster child satisfies the requirements set forth in paragraph (b) of 1.1521 with respect to the taxpayer) of the taxpayer.