Hello I am totally alien to U.S health care system and I am having difficulties understanding things like "suppression of a claim" and I am not sure about what "claim" means also.

Where can I find a good explanation of these things ? 

Thank you.

"Claim" is an application for benefits provided by an insurance carrier. Individuals must file a claim so that the provider of a service can get paid by the insurance. Insurance company may or may not approve a claim. Often the service providers (doctors, hospitals) file the claim on behalf of the patient.

If you are referring to "SupLOS" in the Claims data set - my understanding is the value indicates whether the LengthOfStay field is NULL due to de-identification or because  of some other reason.

Hope this helps