Boundaries
Etymology
From "boundary," from "bound" (a limit or edge), from Old French bodne, from Medieval Latin bodina "a marker." The physical sense of a border is old; the psychological and relational sense — "personal boundaries" — is a 20th-century development from therapy and family-systems theory. Flag the interpersonal meaning as a recent extension.
noun · /BOWN-duh-reez/
The limits a person sets on how others may treat them or make demands of them.
What it names
A handle, now central to how people talk about relationships, for defining where you end and another begins — what you will and will not accept — as an act of self-protection rather than rejection.
Example
Setting a boundary meant telling her mother she would no longer take work calls during dinner — and then not answering.
Related idea
Distinct from an ultimatum: a boundary states what you will do to protect yourself ("I will leave the room if the shouting starts") and is enforced on your own behavior, while an ultimatum tries to control the other person ("stop shouting or else"). The popular blurring of the two turns self-protection into a tool of pressure.