A pre-existing condition is any illness or injury, physical or mental condition, that you have suffered before the effective date of your health insurance coverage. Many health insurance providers will have a clause that excludes pre-existing conditions. Most will also list the pre- existing conditions you may have and still be covered.
Sometimes the insurance company will cover the pre-existing condition, by giving you a higher premium, extended deductible and/or waiting-period. You can also request the underwriting team to evaluate your case during the renewal of your policy.