A Bivens claim, named for Bivens v. Six Unknown Named Agents of Fed. Bureau of Narcotics, 403 U.S. 388 (1971), is a judicially created Constitutional claim which is outside the purview of the Federal Tort Claims Act. See 28 U.S.C. S 2679(b)(2)(A).
Prior to this judicial decision there was little effective recourse to blatent constitutional violations by federal agents and authorities.
E.g. A claim alleging various constitutional violations against Secret Service or FBI Agents in their individual capacities.