A boundary is a line (usually invisible – prison would be an example of a visible boundary) that separates a person from all other people.

Each person is responsible for his or her own boundaries.

Here are indications of poorly defined boundaries:

Sharing intimately on a first meeting.
Falling in love with anyone who reaches out.
Being preoccupied with someone.
Going against what you know is right to please someone.
Hoping someone you meet will have poor boundaries.
Trusting blindly.
Accepting food, gifts, touch, or sex you do not want.
Taking as much as you can get for the sake of getting.
Giving as much as you can give for the sake of giving.
Letting someone be in charge of your life.
Allowing someone else to say what you feel and see.
Believing someone can and should anticipate your needs.
Being moody and withdrawn because you are not getting enough attention.
Expecting people to read your mind and know what you want or need.
Habitually stealing the agenda, taking center stage, occupying the spotlight.
Falling apart to get care.
Eating for destructive reasons or with destructive results.
Sex for pain or to express aggression.

Cloud and Townsend book “Boundaries” is essential reading on this topic.

(The above list is collated from a variety of sources and over so many years and from so many places. I’d love to acknowledge all the sources and would if I had them.)