What is the meaning of the term “res judicata”?

In Canada the term “res judicata” is often used for what may more appropriately be called “cause of action estoppel”. In Ricco v. Ryan 2007 Can LII 44181; [2007] O.J. No. 4030, Quigley J. stated at paras. 25 and 26:

[25] Res judicata prevents the re-litigation of matters that have already been determined by a court of competent jurisdiction. The doctrine is founded not only on the principle that the same party should not be harassed twice in litigation for the same complaint, but also that there is a societal value in the finality and conclusiveness of judicial decisions: see Angle v. M.N.R., 1974 CanLII 168 (S.C.C.), [1975] 2 S.C.R. 248 at 267.