Woolf isn't all mysterious about the title of A Room of One's Own; she really lays it right out there. The point of her essay is that women—and all writers—need to have rooms of their own. Preferably with locks.
These private rooms give women the ability to think independently and without interruption. And this simple, practical title goes along with Woolf's thesis: that it's the simple, practical, material things that are most important when you're trying to figure out how to let genius flourish—or flow like a river. Check out "Symbols" for more on this.