Final answer:
A health issue that existed prior to enrollment in an insurance plan is called a pre-existing condition. The ACA has changed the insurance landscape by prohibiting denial of coverage based on these conditions.
Step-by-step explanation:
A health issue that existed prior to enrollment in an insurance plan is called a pre-existing condition. Insurance companies have historically used these pre-existing medical conditions to determine if an individual is high risk, which could lead to higher premiums or denial of coverage. The Patient Protection and Affordable Care Act (ACA), often referred to as Obamacare, made significant changes to how these conditions are treated within the health insurance market, banning the practice of denying coverage based on pre-existing conditions and working to expand coverage to more Americans.