Vim Directory Structure

autoloadfor standard Vim autoload scripts
compilercontains Vim scripts for specific :compiler‘s. I.e options for errorformat.
ftpluginVim plugin scripts for specific filetypes.
indentautomatically compute the indent for a type of file.
keymapKeymap files for vim
langlanguage files for vim
macrosdefined macros to test for vi compatibility
plugincontains standard vim plugin scripts
syntaxsyntax highlighting
toolsprograms that work with vim, i.e vimspell
tutorhands-on tutorial for vim
aftervim will load stuff in after after everything else

All files ending in .vim in this directory and subdirectories will be sourced by Vim when it detects the filetype that matches the name of the file or subdirectory.

Taken from