(religion, Wicca) A religious tenet held by some Wiccans, stating that whatever energy, positive or negative, a person puts into the world will be returned threefold.

(mathematics education) A rule stating that, if two ratios are equal, then the denominator of the second equals its numerator times the reciprocal of the first ratio: if a/b=c/d then d=(bc)/a.

(statistics, singular only) Synonym of the 68-95-99.7 rule

(Internet slang, fandom slang, informal) The proposition that there are pornographic depictions of anything and everything, especially as fan art on the Internet.

(law) A notion of what should "count" as law.

(sports) A rule requiring that a player receive medical attention before continuing to play if he is bleeding or there is blood on him or his clothes.

(Internet slang, fandom slang, informal) The proposition that it is possible to find genderswapped versions of every fictional character, especially as fan art on the internet.

(photography, film, visual arts) A normative rule that an image should be mentally or representationally divided in three horizontally and diagonally, and that the focus of the image should not be in the center of the resulting shape.

A doctrine in antitrust law which applies to contracts which "unreasonably" inhibit trade.

The ecogeographic principle that, within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, and species of smaller size are found in warmer regions.