The alternate valuation date is the date six months after a decedent's death which, if the executor elects it under Internal Revenue Code section 2032, replaces the date of death as the valuation date for the entire gross estate. The default rule is the date of death: Treasury regulation 20.2031-1(b) states that the value of every item includible in the gross estate "is its fair market value at the time of the decedent's death, except that if the executor elects the alternate valuation method under section 2032, it is the fair market value thereof at the date, and with the adjustments, prescribed in that section."
Section 2032's own heading is "Alternate valuation," and the date form is the IRS's usage: the Instructions for Form 706 use it throughout and the return's asset schedules carry an "Alternate valuation date" column. A reader who also meets the phrase applicable valuation date in section 1014(a)(2) is looking at the same moment described from the income-tax side, where it supplies the heirs' basis.