Facebook was a social networking site.
In 2009, after the Torchwood Three team accidentally drove off the Severn Bridge, they heard a mysterious voice under the water. Back at the Hub, Ianto Jones stated that it was hit on Facebook. (AUDIO: Submission)
When the Twelfth Doctor mentioned that the sonic screwdriver had no effect on wood, Maebh Arden said that the trees could communicate between one another, if only just a little. The Doctor sarcastically asked Maebh if she thought the trees communicate by some form of tree-Facebook. (TV: In the Forest of the Night)