Typically, 17 (or even 16) year olds can emancipate from their parents if they feel it's a disadvantageous environment to be living in.
The courts, however, won't let that person emancipate unless they can show that they can fully support themselves. In other words, they'll need income and be able to live on their own in an apartment. If a girl is just trying to emancipate to move in with her boyfriend to spite the parents, the courts usually say no.
But yes, pretty much what TwiddleMuffin said up there. They no longer have a legal guardian (parental or otherwise).
A minor thats off on their own, they aren't in custody of a guardian. They have a job & they live somewhere else.