what exactly is a single mother? what's your opinion?

Update***
Thank you for your opinions. This post was made because my brother and his girlfriend split up and she is on Facebook saying she's a single mother. My brother moved 200 miles from home and ALL of his family to be with his daughter. He knows no one in the town and is staying there even after they split up in order to see and provide for his daughter. He works full time and takes his daughter all the time and even pays some of the bills still. Though he's no longer in that home. To me, that does not make her a single mother. It just makes her a mother and she is single. 
My mother was a single mom because my dad was ghost for years. So it's offensive to claim that title when my brother is a dad always. 
If you aren't with the father of your child but he helps 100% with time and money, are you a single mom? 
Some say a single mom is just a mom with no sig. other 
Others say a single mom is a mother with no support or help from the biological father. 
What's your opinion?