Shipper is a nickname for someone who wants to see two fictional characters get together.
The prefix added to shipper is the sign of what pairing they like, for example;
PokeShipper = Somebody who wants to see Ash and Misty get together.
AdvanceShipper = Somebody who wants to see Ash and May get together.
ContestShipper = Somebody who wants to see May and Drew get together.
PearlShipper = Somebody who wants to see Ash and Dawn get together.
OrangeShipper = Somebody who wants to see Tracey and Misty get together.
NegaiShipper = Somebody who wants to see Iris and Ash get together.
AmourShipper = Someone who wants to Ash and Serena get together.
A fanatic is a purely single-minded, overzealous person who is tremendously extreme about something.
A PokeShipper fanatic is somebody who either mentally became Ash or Misty, and wants the two to get together so badly that they show deranged behavior on the internet as a result.