The contestability period is the time, usually two years, during which the insurance company could contest a claim if it believes you committed fraud on the insurance application.
If the insurance company finds that you did not disclose all of the relevant information about your medical history, such as symptoms you may have experienced, the insurer could void the contract and refuse to pay the claim, even though you have already paid premiums.
If your insurance company denies your claim, it might cancel the policy and return the premiums paid to your beneficiaries. Premiums would not be returned in cases of fraud. The contestability period applies even if leaving out the information was an oversight and not done intentionally.
However, the insurance company cannot deny a claim after the contestability period has passed, except in cases of fraud.
No matter what type of insurance you are applying for, be sure to answer all questions on the application fully and honestly. If you don't, your policy could be cancelled and any claim you make in the future could be refused.