Fan - a fan is someone who likes something or someone.
Fandom - a fandom is a group of people who like the same thing.
Consumer - a type of fan who isn't obsessed with the thing they like but they still like to talk about it.
Enthusiast - they do everything the consumer does but is a little bit more extreme and does things like buying merch.
Fan - they do everything the consumer and enthusiast does but they are obsessed and they live and breath the thing they are a fan of.
Producer - love the thing so much that they recreate it.
I'm a fan of Dan (Danisnotonfire) and Phil (amazing phil) (Phan) and I'm a part of the Phandom. I buy Phan merch, watch all of their videos and follow them on social media. I talk about Phan with my friends and we use references like "pro tip" and "don't cry craft!". (You probably don't understand those references and now think I'm really weird) Members of the Phandom often call ourselves Phan trash and ship Phan (Phil tops ;)). Shiping something is when you find two people that you really want to be in a relationship. "Don't cry craft!" and "pro tip" comes from an April fools day prank. Phan made a joke channel called Dan and Phil crafts which had a video where they said "pro tip" a lot and at the end they said "and remember don't cry craft!".
Another fandom is the My Chemical Romance (MRC) fandom. People in this fandom are called Killjoys. My Chemical Romance is a band who broke up three years ago on 23rd March. Every year on 23rd March Killjoys like to listen to one of their songs called Welcome to the black parade. They listen to this song because it's so sad that they literally can't listen to it any other day. Killjoys can recognize this song from the first note. Killjoys ship the members Gerard Way and Frank Iero (Frerard) (Frank tops ;)). Some killjoys are so obsessed that they can tell what year a picture of Gerard Way was taken in depending on what colour his hair is.