Physical Boundary
A physical boundary is the limit you set around your body, your personal space, and your need for rest, touch, and privacy. It says who can be close to you and when.
Someone hugs you when you wanted a handshake, and you let it happen because pulling back felt rude. That is a physical boundary getting overridden. The same thing happens when you skip lunch to finish someone else's task, or stay at a gathering long past the point your body wanted to leave.
For people who learned to fawn, the body's signals get quiet. Reading other people's comfort became more important than reading your own, so the nudge that says too close or too tired arrives late or not at all. Tiredness, hunger, and the urge for space are data, and they get easier to notice once you start treating them as real.
A physical boundary can be small. Stepping back to a distance that feels right. Saying you would rather not be touched today. Leaving when you are done. None of these require a reason the other person agrees with.