The Latin phrase you have in mind is "ratio decidendi." Its literal
meaning is "reason for deciding." It is typically the term used to
describe the specific rationale for a court's decision, as opposed to
other statements of the court that are not necessary for its decision
(which are known as "obiter dicta").
Here is a somewhat more detailed definition of the term in laymen's
terms, from an orientation document for new students at Emory U. law
"The fancy Latin phrase for ?holding? is ratio decidendi, which
translates roughly to the ground or reason of decision.
"It is a common misunderstanding to think of ?decidendi? as being the same
word as ?descend? (one sometimes hears reference to a case?s ratio descendi??
a term that just does not exist). This is incorrect; ?decidendi? is
etymologically related to ?decision,? not ?descend.? But you can see how in a
system based on stare decisis that misconception would arise. The holding,
the ratio decidendi, of a prior case is its central feature from the
point of view of those who come later and are trying to determine ?the
law?; it is what
descends from one case to the next. But to say that the holding descends
does not tell us what a holding is. The true meaning of ?decidendi? provides
a better clue: it suggests that the holding is the basis for the decision, the
thing(s) on which the result turned."
Emory U. Law School: Academic Orientation (at page 18)
Of course, the phrase can and is also sometimes informally used to
means the "reason for deciding" in other contexts as well.
I recognized the phrase from your description and my research was
focused on finding the most useful definition for you. To do that, I
used the following Google search:
"ration decidendi is OR means"
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