Fanfic: The term 'fanfic' refers to works of fiction
modelled after anime characters and stories.  A fanfiction
story may take characters introduced in animated videos or
manga and expand upon them, placing them in different worlds
or in events not covered by the original story.

If you are interested, you can find many fanfiction stories
and images at the newsgroup 'rec.arts.anime.creative', as
well as many fan sponsored webpages.  Just set your search
engine on 'fanfic'.

Using R.A.A.C.'s admittedly generous specifications, a fanfiction conveyed in text instead of in illustrations can be:
   1) an episode which could fit in the actual storyline, 
   2) a cross-over between two or more different animes,
   3) a parody of the original,
   4) an entirely original story but with 'anime look-and-feel',
   5) skits, impressions, take-outs, and just plain fun.

"Macho Caballo" is classified as a 'semi-original' fanfiction,
in that it takes a recognizable element (shape-changing 'cursed'
springs) from a known work (Ranma 1/2) and incorporates that 
element in a new story with new characters.


Manga: Japanese comic books.  I think the term is taken from 
sketch pads used by tale-tellers in earlier days who illustrated 
their stories with sketches.  

Anime: Animated video, sort of high-brow cartoons, of which
the leading producer is Japan.  The difference between 'true
anime' and commercially manufactured gruel is a matter of
dispute even to died-in-the wool anime fans - the general
requirements are that the anime feature characters with more
than one dimension, a direction or point to the plot, and
enough visual joy to make the viewing worthwhile.  Japanese
anime seems to provide fuel for hoards of fan-fiction writers
who want to enjoy the characters and situations long after
the viewing is done.

Anime has been termed the 'art-form of the next century' -
Okay, I was the one who said that, but what the heck...