| GP also refers to a General Practitioner, particularly in Australia but also in use in other parts of the world1. Basically a doctor, running a surgery, providing "general" health care. They should be your first line of defence for any ailment, unless it is critical, at which point you should go to a hospital.
They often bulk bill their treatments, passing on great cost savings to the patient, and get the appropriate Medicare rebate from the government.
Services include vaccinations, treatments of non-critical wounds, referrals to specialists, x-rays and many other services for general health maintenance of a large population.
In Australia, nowhere near enough people visit their local GP. They are happy to go to hospital to have something non-critical fixed, when in fact you could get the same treatment at a GP. However, Australians like to build up a good rapport with one specific GP, probably one that the family has "always" been to.
One downside to the GP is that they DO bill. The charges that the patient actually incurs is actually only 15%, with the other 85% covered by Medicare.
GPs are good. Visit them more often than you do. You'll be healthier for it!
1 - RPGeek says re gp: I don't think the use of the acronym is specific to Australia; I've heard it frequently here in Canada. (It's also in common use in the UK) | 
