A one participant 401(k) plan is sometimes called a Solo(k), Uni(k) or Individual(k). They are all the same type of plan. The Solo(k) plan is a Traditional 401(k) Plan covering a business owner(s) or the owner(s) and his or her spouse. These plans have the same rules and requirements as any other 401(k) Plan. It is imperative to note that it must be a set up under a business and if the business hires employees, they must be monitored and if they have an employee that meets the eligibility requirements, they are full Traditional 401(k) Plan and all testing rules apply.