(physics) A model (not believed to be literally true) developed by physicists Theodor Kaluza and Oskar Klein that attempted to combine gravity and electromagnetism by adding a fifth dimension to our four-dimensional spacetime.

(finance) A theory of asset pricing serving as a framework for the arbitrage pricing model.

(linguistics) A theory that posits a common syntactic structure for different lexical categories. Each phrase (XP) is the projection of a head (X) and may optionally include a specifier (sister of X-bar, daughter of XP), adjuncts (sister and daughter of X-bar) and complements (sister of X, daughter of X-bar).

(economics) Theory that the price of an object is determined by irrational beliefs and expectations of market participants, rather than intrinsic value; i.e. that one can make money by buying something for the sole reason of selling it to some one else for a higher price.

(astronomy) A cosmological model of the universe in which matter is continuously created as the universe expands

(criminology) A criminological theory stating that signs of urban decay (e.g. broken windows, graffiti) signal that an area is not monitored, encouraging more destructive criminal behavior.

A theoretical explanation for departures from ideality in solutions of electrolytes.

Information theory adapted to deal with information held and/or handled by quantum systems, i.e., in which information is measured in qubits instead of classical bits.

(physics, chemistry) A method of determining the structure of a molecule by assuming that electrons are not fixed to bonds between individual atoms

(chemistry, physics) A description of various properties of transition element complex compounds that compares the effects of its ligands to that of neighbouring atoms in a crystal