A holiday, or a vacation, was an excursion to a location for leisure.
When the Sixth Doctor announced to Peri that the TARDIS suddenly had no faults, saying that he didn't know what to do with himself, Peri convinced him to take a holiday. The Doctor at first objected, saying that "Time Lords don't take holidays", he ultimately took to the idea, and selected Tranquela as their destination. (AUDIO: The Ultimate Evil)
The Eleventh Doctor promised to take Clara Oswald on a "proper holiday" only for him to wipe his memory while tampering with the telepathic circuits. After Clara helped him restore it via the Twelve Hundred Year Diary, the two went off on their holiday. (TV: The History of the Doctor)