Feltson is a shorthand for Felton/Watson. Tom Felton and Emma Watson are both from the movie Harry Potter. Felton plays Draco Malfoy while Watson plays the role of Hermione Granger. They met on set while filming. Both have been rumored to have dated each other somewhere along those years thus resulting to a great number of fans shipping them together resulting to numerous fan videos, fan pictures and even fanfictions, gathering legions of supporters across the world.
Feltson is also known to be the real life counterpart of the popular fanfiction fandom Dramione (Draco/Hermione), although they are different.
Those behind the scenes video from the yuleball where Tom Felton asked Emma Watson to dance suggested so much of Feltson and Dramione.