What is constitutional standing and what is the test for standing?

Constitutional standing refers to the requirement that parties suing in federal court establish that a Case or Controversy exists within the meaning of Article III of the United States Constitution. Constitutional standing requires (1) that the plaintiff have suffered an injury in factthat is, an invasion of a legally protected interest which is (a) concrete and particularized and (b) actual or imminent, not conjectural or hypothetical; (2) that there is a causal connection between the injury and the conduct of which the plaintiff complains; and (3) that it is likely ... that the injury will be redressed by a favorable decision. Lujan v. Defenders of Wildlife, 504 U.S. 555, 56061, 112 S.Ct. 2130, 119 L.Ed.2d 351 (1992) (internal citations and quotation marks omitted).