A more thorough explanation:

A preexisting condition is a physical or mental health condition that existed before the effective date of a medical insurance policy. If symptoms of the condition were present during the period before the policy was effective, coverage for later treatment for such a condition is usually excluded. For example, if someone has a history of heart disease and then buys a health insurance policy, any future treatment related to their heart disease may not be covered. Another example is if someone has a chronic illness like diabetes before buying a health insurance policy, any treatment related to their diabetes may not be covered. These examples illustrate how a preexisting condition can affect coverage under a medical insurance policy. Insurance companies may exclude coverage for preexisting conditions to avoid paying for treatment that was already needed before the policy was in effect. A preexisting condition is an important concept in the world of medical insurance. It is important for individuals to understand whether their medical conditions are considered preexisting before purchasing a policy. This can help them make informed decisions about their coverage and avoid unexpected medical bills.