Short answer: Employer-paid (non-contributory) benefits are funded by the employer and usually cover all eligible employees automatically. Voluntary (employee-paid) benefits are offered through the employer but paid by the employee, often via payroll deduction, and are elective.
The distinction is who pays. Employer-paid or ‘non-contributory’ benefits; common for basic life or sometimes base medical; are funded by the company and typically enroll everyone eligible, which also helps meet participation rules. Voluntary (or ‘contributory’) benefits, like additional life, disability, accident, critical illness, dental, or vision; are made available through the employer’s group but paid by the employee, usually via convenient pre- or post-tax payroll deductions at group rates. Voluntary benefits give employees choice and access to group pricing without adding employer cost, though higher amounts may require evidence of insurability.