Slacks implies pants of certain materials which are not part of a suit (jeans are not slacks, and you would not refer to the pair of trousers that came with a suit as slacks.) It is also more common to use slacks to refer to pants worn by women, while men would wear trousers.
Health care safety net providers are those that have a legal mandate or mission to offer medical care to all patients, regardless of their ability to pay, and have a substantial number of patients who are uninsured or on Medicaid.
Any organization, public or private, that pays or insures health or medical expenses on behalf of beneficiaries or recipients, such as commercial insurance companies, Medicare, and Medicaid. A person generally pays a premium for coverage in all such private and in some public programs.