What combination characterizes a hybrid rocket motor design?

Solid fuel grain combined with a liquid or gaseous oxidizer

The hybrid rocket concept represents a middle ground between pure solid and pure liquid systems by combining elements of both. Specifically, a hybrid motor utilizes a solid material for the fuel component, which is typically housed in the motor casing in a fixed grain structure, similar to a solid rocket. However, the oxidizer component is stored as a liquid or gas, which is then injected into the chamber to meet the solid fuel surface. This configuration retains some simplicity because only one component needs complex fluid handling, often allowing for throttling and restarting capabilities borrowed from liquid designs, as seen in the $ ext{SpaceShipOne}$ vehicle using solid $ ext{HTPB}$ rubber with nitrous oxide.