Reservation of rights in the context of insurance claims is when an insurer sends a reservations of rights letter to the insured stating that it does not waive a right merely because they do not affirmatively assert it in the present, but rather holds these rights to be used at a later period. For example, an insurer may reserve the right to contest coverage or recover the costs of defense against an insured. The rights reserved to each party are typically set forth within the insurance policy and will vary depending on the type of insurance you have, and which respective state laws govern.
Your overall policy and state regulations will determine the legality of certain reserved rights and when they can be used for or against you. An experienced insurance claims attorney can help you with this analysis to give you the best strategic use of your reserved rights or to not be caught off guard by an assertion of a reserved right by your insurer.