Is there a difference between heartburn and gerd?

Yes. Heartburn is a common symptom of gastroesophageal reflux disease (gerd). Not all heartburn is gerd( 95%+ is) and not everyone with gerd has heartburn.
Really the same. Some doctors may call more regular episodes of heartburn gerd i.e. Daily as opposed to episodic heartburn that you get from eating too much pizza.