Controlled group means, in connection with any person, a group consisting of such person and all other persons under common control with such person, determined under 4001.3 of this part. For purposes of determining the persons liable for contributions under section 412(2) of the Code or section 302(b)(2) of ERISA, or for premiums under section 4007(e)(2) of ERISA, a controlled group also includes any group treated as a single employer under section 414 (m) or (o) of the Code. Any reference to a plan's controlled group means all contributing sponsors of the plan and all members of each contributing sponsor's controlled group.
29 CFR § 4001.2
For purposes of this chapter (unless otherwise indicated or required by the context):