When you request life insurance coverage, you answer some questions on the application, some of those questions have to do with your health.
The insurance company needs to determine how healthy you are, and how long you may live, before they decide to offer you life insurance coverage.
When they ask about any diagnosis, they are asking if you have been diagnosed (by a doctor) with any health problems, such as, HIV/AIDS, diabetes, high cholesterol, heart or kidney problems, or any type of medical diagnosis.
This information helps the insurer to determine if they can insure you for life insurance, how much life insurance they can offer you, and what your rate should be for your life insurance policy.
If you have been diagnosed with a serious medical condition, you may find it difficult to get approved for life insurance, or your rate for coverage may be much higher than a standard-rated risk for life insurance.
If you have questions, ask your life insurance agent or the insurance company for a more specific explanation of what is meant by being "diagnosed with anything".