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.
While many of these clinics serve substantial numbers of low-income people, not all of their users are uninsured. For example, although 88 percent of the patients served by federally qualified health centers (FQHCs) have incomes below 200 percent of the federal poverty level, only 39 percent are uninsured.