Lengos Four was the homeworld of the Lengo. The Eleventh Doctor noted it was a very oddly named planet considering that it was one of only two planets in the star system.
After a wormhole had brought a rogue Lengo into Maisie Thompson's house, the Doctor took her to Lengous Four via the wormhole to retrieve the Christmas presents they had taken with them. After the Lengo had been made aware of their error, they quickly returned the presents, Maisie gifting one to them. Inspired by the act, the previously solitary Lengo species created their own gift-exchanging festival. Thirty-four years after she first met the Doctor, he brought Maisie back to Lengos Four to see the festival for herself. (PROSE: The Gift)