Fan Flutter?
barka, I suspect that you mean "fan flutter" - which means he's technically right, but being a bit pedantic.
All airfoils/wings, including fan blades, have aeroelastic behaviour. That is, they must be considered to be non-rigid items (they bend under load) and the interaction of the bending under load must be considered with the change to the load caused by the bending.
Aeroelasticity is usually a bigger concern with the aircraft wing - as this is the most flexible of the various wing-like items we must consider. But fan blades, especially in the larger bypass engines, are pretty big, and are attached to the disc with relatively small root sections. So if the blade were to start to flap then it might be that the aerodynamic forces were powerful enough to overcome the structural resistance to bending, and the blade might fail.
In order to reduce the amount of blade deflection and vibration, manufacturers used to add 'snubbers' to the blades at about half their length. These are really parts of a ring around the engine, with the section added to each blade, so that the neighbouring blades stiffen each other. More modern engines/blades, which use more advanced blade materials, don't use these (they cause penalties to the aerodynamic efficiency of the blade).
Hope that helps.
By the way, what kind of engineer?