What does "homeless" mean?

Here’s a link to an interview with the author of “A Girls Guide to Homelessness”. 

(http://finance.yahoo.com/family-home/article/112801/fight-to-rejoin-middle-class-usnews)

It’s a great story that highlights the fact that people who are homeless all have a different story. We also don’t always see the folks who are homeless in our midst. Brianna says in the interview “There's also a misconception about what "homeless" means. Do you have to be panhandling? Or sleeping on a park bench? A lot of people think it doesn't count if you're living out of a vehicle, but if they were living out of a vehicle, they might think otherwise.” Do you think someone who is living out of their car is homeless? What about someone who is living in a motel? Share your thoughts!