Definition of Employer in 402(e)(4)

[Guest newtobenefits]

402(e)(4)(D)(ii) explains that for Net Unrealized Appreciation purposes certain plans "maintained by the employer" are aggregated together to determine whether participant has taken a lump sum distribution.

What is the definition of employer here? Would it include all control group members?

The definition in 414(b) does not list 402 as a section to which it applies.

Any help is appreciated.