From AMS Glossary
A hydrodynamical paradox arising from the neglect of viscosity in the steady flow of a fluid around a submerged solid body.
According to this paradox, the submerged body would offer no resistance to the flow of an inviscid fluid and the pressure on the surface of the body would be symmetrically distributed about the body. This paradox may be traced to the neglect of the viscous forces, which are indirectly responsible for fluid resistance by modifying the velocity field close to a solid body.
Birkhoff, G. 1950. Hydrodynamics. 10–22.