Question

In your article about the enactments of the Sages, I came across some acronyms. I’d be grateful if you could explain what “passive omission” and “positive action” mean.
I’ll quote the passage:
“It should also be noted here that according to the law, the Sages uproot a Torah law only through passive omission, or through positive action as a temporary measure, like Elijah at Mount Carmel (see Ran on Nedarim 90b, who says that according to the rules, even uprooting through positive action is possible as a temporary measure). Yet in certain cases we find among the medieval authorities (Rishonim) that the Sages had authority to uproot a Torah law even through positive action and permanently. Clearly, such a step is taken in situations of critical need, and we see that the Sages can deviate from the formal rules that allow them to uproot only through passive omission or only temporarily. If so, even in our time there is room to do so if the times require it.”.
Thank you in advance!