It stands for FokaStudio's Ender Expansion
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FokaStudio's Ender Expansion (or FSEE for short) is a Minecraft 1.19 worldgen datapack that focuses on rehauling The End dimension in a new, unique and fairly lively way.
FSEE started off as a direct port of Far End, for a server called Azalea Network (today known as Riptide Network, you should definitely check it out!), but grew into its own independent project as time passed.
Needless to say, the pack is now nothing like its predecessor. Everything has changed drastically, with more changes to the original being made each day.