(a) "Employees" means the employees, officers, and agents of any person, firm or corporation or of one or more corporations having business interests in common.
(b) "Employer" means the person, firm, corporation or one or more corporations having business interests in common, and includes any organization of such employers.
(c) "Retirement system" or "system" means a non-profit corporation or trust formed for the purpose of providing pension benefits.
(d) "Pension benefits" means benefits provided by a retirement system for members retiring by reason of age or length of service, or both, and benefits permitted by section four thousand six hundred three of this article.