Health insurance – also referred to as medical insurance or healthcare insurance – refers to insurance that covers a portion of the cost of a policyholder's medical costs. How much the insurance covers (and how much the policyholder pays via copays, deductibles, and coinsurance) depends on the details of the policy itself, with specific rules and regulations that apply to some plans. If you don't have health insurance and you end up needing medical care, you can be left with insurmountable medical bills or even face situations in which medical providers refuse to treat you. Only screening and stabilization in a hospital emergency department are guaranteed if you're uninsured (and the hospital and providers can still bill you for the costs). Other than that, it's up to the provider to decide whether to treat you if your ability to pay for the care is in question. Even if your out-of-pocket costs seem high under the health plans available to you, having a health insurance card might make the difference between being able to obtain care or not. It's also important to understand that you cannot just purchase health insurance when a medical need arises. Regardless of whether you're buying your own coverage or enrolling in a plan offered by an employer, there's an annual open enrollment period that applies, and enrollment outside of that window is limited to special enrollment periods triggered by qualifying events.