Filet is how American English often spells fillet: a piece of fish or meat with the bones taken out, so you can eat it in clean pieces. You will see it most on menus in filet mignon — a thick, soft cut of beef that restaurants treat as a treat. Though actually Americans are not perfectly tidy about this. The French-looking filet (often said more like "fi-LAY") is the one they put on fancy menus; they still often write fillet for fish, and the verb "to take the bones out" is almost always fillet, not filet. In Britain you will nearly always see fillet, said more like "FILL-it". Same food, two spellings, two sounds. It is not a different dish, and it is not a little file of papers.