A terminal disclaimer (TD) is a statement filed by a patent owner in which the owner disclaims or dedicates to the public the entire term, or terminal part of the term, of the patent granted. See 37 C.F.R. 1.321. Typically, a disclaimer is filed in cases in which a claim or claims of a pending application would have been obvious in light of at least one claim in an earlier-filed issued patent—also referred to as a non-statutory double patenting rejection.
In other words, when a terminal disclaimer is filed in a pending application to overcome a non-statutory double patenting rejection, the applicant states that the issuing patent will have the same term as the previously issued patent and that both patents will be commonly owned. If at any point in time, both patents are not commonly owned, patent(s) may be rendered unenforceable.