Based on the provided knowledge sources, there isn't a clear distinction between a "Hydra client" and a "Hydra OAuth client". However, in the context of Ory Hydra, an OAuth client (also referred to as OAuth 2.0 client) is an application that securely authenticates with the authorization server to obtain access to an HTTP service. These clients can be confidential or public, with confidential clients being able to use registered client secrets to authenticate, while public clients are unable to use registered client secrets. OAuth clients can be managed using the Ory Console, Ory SDK, Ory CLI, and Ory REST APIs [source](https://www.ory.sh/docs/hydra/guides/oauth2-clients). The term "Hydra client" isn't explicitly defined in the provided sources, but it could potentially refer to any application or service that interacts with the Ory Hydra API. This could include OAuth clients, but also other types of clients depending on the context. For more specific information about the different types of clients in Ory Hydra, you may want to refer to the official Ory Hydra documentation.