Opt-Out Plan

What Does Opt-Out Plan Mean?
A type of 401(k) plan that automatically enrolls the employees of a company to save for their retirement. Eligible employees of a company with this policy are enrolled in the plan at a default contribution rate, usually around 3% of wages, and funds are directed into a default allocation. Employees can change the terms of the plan or opt out completely if they don't want to participate. This differs from a typical 401(k) in that retirement savings will continue to accumulate without any action from the participant.

Also known as an "automatic 401(k)".

Investopedia explains Opt-Out Plan
Due to the complexity of some 401(k) forms and the stress of allocating the funds, some people may choose not to participate in a plan at all. An opt-out plan does this work for the employee, while still allowing him or her to change the terms as needed.