What is "standing" and "lack of standing"?

Quick answer: Something serious that may nix a pending or contemplated lawsuit without regard to the merits because the plaintiff (or the petitioner or intervenor in a child custody proceeding) did not have the right to bring the action or get involved in a pending proceeding.

In laymen's terms "standing" means that you can't get the judge to play umpire if you don't have a dog in the fight. Stated differently, you must have a real complaint against someone that a court can do something about under the law. Of course, such a general definition won't do for legal purposes. Nor is it enough for standing purposes to simply assert a claim or complaint. The right to make that claim must be recognized under the law.

Here is how the Dallas Court of Appeals defined standing as a general principle. (Note that standing for grandparents and non-parents in suits affecting the parent-child relationship is governed by the Texas Family Code, i.e. by statute, rather than by general standing principles found in case law):

Standing is a party's justiciable interest in a controversy. See Nootsie, Ltd. v. Williamson County Appraisal Dist., 925 S.W.2d 659, 661-62 (Tex. 1996); Town of Fairview v. Lawler, 252 S.W.3d 853, 855 (Tex. App-Dallas 2008, no pet.). Without a breach of a legal right belonging to a plaintiff, that plaintiff has no standing to litigate. Cadle Co. v. Lobingier, 50 S.W.3d 662, 669-70 (Tex. App.-Fort Worth 2001, pet. denied). Only the person whose primary legal right has been breached may seek redress for an injury. Nauslar v. Coors Brewing Co., 170 S.W.3d 242, 249 (Tex. App.-Dallas 2005, no pet.). In reviewing standing on appeal, we construe the petition in favor of the plaintiff, and if necessary, review the entire record to determine if any evidence supports standing. See Tex. Air Control Bd., 852 S.W.2d at 446.

Lack of standing is a fundamental issue that is difficult, if not impossible, to fix. It can provide a basis for an order being thrown out on appeal if the trial court entered it in favor of a party who did not satisfy the standing requirement. Standing is treated as jurisdictional. When there is no jurisdiction, the hands of the judge are tied. All the court can do under such circumstances is dismiss the lawsuit, or the appeal, whichever applies, or to dismiss the party without standing (in a suit with multiple other parties). As put by the Dallas court, with citations to caselaw:

Standing, a necessary component of subject matter jurisdiction, is a constitutional prerequisite to maintaining a suit under Texas law. Tex. Ass'n of Bus. v. Tex. Air Control Bd., 852 S.W.2d 440, 444-45 (Tex. 1993). A standing defect cannot be waived and can be raised for the first time on appeal. Id. at 445-46. A party's standing to pursue a claim is a question of law that we review de novo. Mayhew v. Town of Sunnyvale, 964 S.W.2d 922, 928 (Tex. 1998).

SOURCE: Opinion of the Dallas Court of Appeals in 05-08-00038-CV