In simplest terms, a qualified retirement plan is one that meets ERISA guidelines, while a non-qualified plan falls outside of ERISA guidelines.
Qualified plans include 401(k), profit sharing plans, 403(b), and Keogh (HR-10) plans.
Tax treatment is the main difference between qualified and non-qualified retirement plans.
Contributions to a non-qualified plan are not deductible to the employer until the employee takes a withdrawal and is taxed on the income.
Employer contributions to a qualified plan may be deducted immediately.