What the heck are boundaries?

I’ve been doing a lot of research on the topic of boundaries and how women in particular have a hard time with them. Many of the women I talk to say they would love to have boundaries but they just can’t set them because it’s too hard or not well received, both at home and at work. The guilt with setting boundaries is so profound that they would rather just say yes knowing deep down that they really should say no. Saying yes comes at the expense of their well-being.