From abstract of an earlier paper co-authored by Reddy > A mode of a predicate designates some of its parameters to be input and the others to be output. ... i

From abstract of an earlier paper co-authored by Reddy > A mode of a predicate designates some of its parameters to be input and the others to be output. ... indefinite modes... in which a resolution interpreter yields answers with free variables. https://www.tib.eu/en/search/id/tema-archive%3ATEMAE84100273082/Transformation-of-logic-programs-into-functional/ https://www.tib.eu/en/search/id/tema-archive%3ATEMAE84100273... Sounds like well-moded means: for given inputs, you get a definite answer, rather than something to be further computed around (like high school algebra with more than one unknown). Fits the context here.