abuse of the writ

if a prisoner deliberately withholds one of two grounds for federal collateral relief at the time of filing his first application, in the hope of being granted two hearings rather than one or for some other such reason, he may be deemed to have waived his right to a hearing on a second application presenting the withheld ground. The same may be true if the prisoner deliberately abandons one of his grounds at the first hearing. Nothing in the traditions of habeas corpus requires the federal courts to tolerate needless piecemeal litigation, to entertain collateral proceedings whose only purpose is to vex, harass, or delay.

Defined by the Supreme Court in - Sanders v. United States, 373 U.S. 1 (1963).