Boundaries are limits an individual sets for themselves. Boundaries can be emotional, physical or mental. It is defined as a permissible and safe way to behave with someone.
Sources:
https://www.theresiliencecentre.com.au/boundaries-why-are-they-important/
https://uhs.berkeley.edu/sites/default/files/relationships_personal_boundaries.pdf
https://www.verywellmind.com/boundaries-in-relationships-and-stress-3144984