A rogue planet is a planet that has broken out of its orbit around a star. However, such a planet may still be capable of supporting life due to geologic activities on it, such as hot gases venting from its interior, forming oases where lifeforms can thrive. The lack of a sun causes rogue planets to exist in a state of perpetual night.
In the TOS: "The Squire of Gothos", Spock described Trelane's planet of Gothos as a "lone planet", implying it was rogue planet. However, Kirk later ordered his crew to take the Enterprise beyond "the point at which we entered [Gothos's] solar system", implying the planet orbited a star instead.