Leg of the weld. Fillet is the part you cut off e.g. a corner...

A fillet is a Boneless cut of Salmon, a Darne is a cross-cut of Salmonin including the backbone.

Filet mignon is French for "cute fillet" or "dainty fillet" of steak. Strictly speaking, it is only a filet mignon if cut from the very top end of the tenderloin.

I think the fillet of steak is the most tender. Its located just on the backbone

The type of cut that is considered a fillet depends on the meat in question. It would either be a prime cut of beef, a cut of fish that doesn't include the backbone or half a chicken breast trimmed.