What is the difference between reflux and GERD

I believe my son has a reflux my doctor also thinks so but now i have been reading about GERD and it seems lile the symptoms are very similar. He does spit up alot and sometimes i can hear the milk coming back up and he is swallowing it back. I.also noticed that sometimes he is trying to swallow something smd then catching on breath sometimes wheezing after feed is that normal? Im kind of freaking out about this GERD.