A Fillet is a curved face of a constant or variable radius that is tangent to, and that joins,two surfaces.

Edge Fillets:-Smooth transitional surface between two adjacent faces

Face-Face Fillet:- Used when there is no intersection between the faces or when there are more than two sharp edges between that faces

Variables Radius Fillets:-Curved surfaces defined according to variable radius.

Tritangent Fillets:- Involves that removal of one of the three faces selected.