Significantly affected plan

Significantly affected plan means a plan that -
(1) Transfers assets that equal or exceed 15 percent of its assets before the transfer,
(2) Receives a transfer of unfunded accrued benefits that equal or exceed 15 percent of its assets before the transfer,
(3) Is created by a spinoff from another plan, or
(4) Engages in a merger or transfer (other than a de minimis merger or transfer) either -
(i) After such plan has terminated by mass withdrawal under section 4041A(a)(2) of ERISA, or
(ii) With another plan that has so terminated.

Source

29 CFR § 4231.2

Scoping language

The following terms are defined in 4001.2 of this chapter: Code, EIN, ERISA, fair market value, IRS, multiemployer plan, PBGC, plan, plan year, and PN.