What you mean by fluid resistance should be the resistance or friction that hinders the relative motion between layers of fluid or the relative motion of moving objects in fluid. Because fluid has a characteristic: when there is relative motion or shear deformation between fluid layers, the fluid will resist this relative motion or shear deformation, so that the fluid gradually loses its relative motion. This kind of shear deformation resistance of fluid, or the characteristic that hinders the relative movement of fluid layers, is called viscosity. It is precisely because of the existence of viscosity that the fluid resistance between fluid layers or between objects moving in fluid and fluid hinders their relative motion. Macroscopically speaking, the relatively fast fluid layer has a drag force on the relatively slow fluid layer, which makes the slow fluid layer faster. The corresponding slow fluid layer will drag the fast fluid layer to slow it down, and finally the motion between the fluid layers will disappear. The force per unit area between fluid layers is called viscous stress. According to Newton's law of viscosity, the fluid viscous stress per unit area is directly proportional to the speed change per unit length along the normal direction of the plane of motion, or the viscous stress is directly proportional to the shear deformation rate. There is a product term in the expression of fluid viscous stress, which is the viscosity coefficient of fluid. Different fluids have different viscosity coefficients. Usually, the viscosity coefficient of the same fluid is also related to temperature. For example, with the increase of temperature, the viscosity coefficient of air increases, while that of water decreases. It can be seen that the viscous stress of the fluid depends on the physical properties of the fluid itself. Different fluids have different resistance effects, and the same fluid has different resistance effects at different temperatures.