Decorum
Etymology
From Latin decorum "that which is fitting," the neuter of decorus "seemly, becoming," from decor "grace, beauty," from decere "to be fitting" — the same root as "decent" and "decorate." Decorum is, at heart, the fittingness of a thing to its context.
noun · /dih-KOR-uhm/
Behavior that is fitting and dignified for a particular occasion or setting.
What it names
A handle for the sense of what suits the moment — the propriety that reads a situation and matches it, rather than following a fixed list of rules.
Example
Laughing was fine at the reception, but decorum called for silence during the eulogy.
Related idea
Distinct from etiquette: etiquette is a fixed code you memorize, while decorum is the judgment of what is appropriate to this occasion, which can require breaking etiquette. Decorum is contextual and about dignity; etiquette is conventional and about correctness.