Class 7 warp drive

From Memory Alpha, the free Star Trek reference.

The class-7 warp drive was a type of warp drive with which Defiant-class starships were equipped, capable of achieving the maximum velocity of warp 9.5. (DS9: "One Little Ship")

One distinctive feature of the class-7 drive was the tri-lobed matter and antimatter injectors.

Though never stated on screen, it is possible that the multi-lobe injectors were indicitive of the "multiple reactant stream injection" technology Starfleet had under development years previous as referenced by Geordi in "Galaxy's Child". The feature was scheduled to be included in the "next class starship".