Definition: Inviscid fluid refers to a type of liquid or gas that is not easily affected by external forces, such as gravity or pressure. This means that the flow of an inviscid fluid does not experience any resistance from the surrounding environment, which can make it difficult for fluids to be used in applications where they need to withstand external forces. Inviscid fluids are often found in environments with high pressures and low temperatures, but they can also be found in more common conditions like rivers or lakes.