Sublight

From Memory Alpha, the free Star Trek reference.

Sublight or space-normal speed is a term that refers to anything below the speed of light, approximately 3 × 10⁸ meters/second.

Sublight is usually used to describe non-warp speeds, typically when either an impulse drive or thrusters would be used as propulsion for a vessel.

Bajoran lightships traveled at sublight speeds. (DS9: "Explorers")