Abuse of Process - Definitions. Phillion v. Ontario (Attorney General)
In Phillion v. Ontario (Attorney General) (Ont CA, 2014) the Court of Appeal quotes from the Supreme Court of Canada on the elements of abuse of process, citing the close relationship that the doctrine has with issue estoppel, and the broad (even primordial) relation that it bears to 'justice':
 The leading case on the doctrine of abuse of process is the Supreme Court of Canada’s decision in Toronto (City) v. C.U.P.E., Local 79, 2003 SCC 63 (CanLII), 2003 SCC 63,  3 S.C.R. 77. Arbour J. explained, at paras. 35-37, that this doctrine represents the inherent and residual discretion to “prevent an abuse of the court’s process” when other doctrines such as issue estoppel may not be available. At para. 35, she adopted the words of McLachlin J. (as she then was) in R. v. Scott, 1990 CanLII 27 (SCC),  3 S.C.R. 979, at p. 1007, as follows:Again, in Phillion, the court commented generally on the nature of abuse of process and that it was only to be found in the clearest of cases:
[A]buse of process may be established where: (1) the proceedings are oppressive or vexatious; and, (2) violate the fundamental principles of justice underlying the community’s sense of fair play and decency. The concepts of oppressiveness and vexatiousness underline the interest of the accused in a fair trial. But the doctrine evokes as well the public interest in a fair and just trial process and the proper administration of justice.
 In my view, the order dismissing the action as an abuse of process must be set aside. Such orders are only to be granted in the clearest cases and only when allowing the action to proceed would bring the administration of justice into disrepute. The motion judge erred in law in concluding that this was a case of relitigation and that it justified the application of the doctrine of abuse of process.. Plate v. Atlas Copco Canada Inc.
In Plate v. Atlas Copco Canada Inc. (Ont CA, 2019) the Court of Appeal attempted to define abuse of process as follows:
 The doctrine of abuse of process provides the court the discretion to prevent re-litigation where necessary to preserve the integrity of the adjudicative process: Toronto (City) v. C.U.P.E., Local 79, 2003 SCC 63 (CanLII),  3 S.C.R. 77, at paras. 42-43, 51; Intact Insurance, at para. 28. Re-litigation inevitably has a detrimental effect on the due administration of justice, as it can lead to inconsistent results, devalue finality, and contribute to the unnecessary expenditure of public and private resources, with no guarantee that the second result will be more accurate than the first: C.U.P.E., at paras. 51-52; Intact Insurance, at para. 28.
 Thus, re-litigation is to be avoided unless the circumstances dictate that re-litigation is necessary to enhance the credibility and effectiveness of the adjudicative process as a whole: C.U.P.E., at para. 52; Intact Insurance, at para. 28. While there is no closed list of circumstances in which re-litigation is necessary, courts will permit re-litigation if in the specific circumstances “fairness dictates that the original result should not be binding in the new context”: C.U.P.E., at para. 52-53; Intact Insurance, at para. 28.