Boundaries can be defined as the physical, mental, emotional, sexual, spiritual, financial, educational, etc., parameters or limits you set for yourself within a relationship; what you will accept and what you will not. They allow you to protect yourself and to achieve appropriate and healthy self-care.
—Arlene R. Taylor

It is quite basic: either you set and implement your own boundaries or others will set them for you—which usually means none, especially if they wish to control you.  
—Arlene R. Taylor