What are "Superfluids"?

Dear student 

Superfluids is another state of matter beside solid, liquid and gas in which matter behave like a fluid with zero viscosity. 
​Superfluidity is the property by virtue of which matter shows frictionless flow at temperature near 0 K. Frictionless flow means that there is no presence of viscosity. Viscosity is internal property of fluid, it is resistance to flow.
For example - it was first discovered in liquid Helium-4. 

Regards