Distributed Application (DApp or DApp) is software that is executed or run on multiple computers within a network. These applications interact in order to achieve a specific goal or task. Traditional applications relied on a single system to run them. Even in the Client-Server model, the application software had to run on either the client, or the server that the client was accessing. However, distributed applications run on both simultaneously. With distributed applications, if a node that is running a particular application goes down, another node can resume the task.
Source: Distributed Application (Dapp)