Cyberspace

Cyberspace was, as the Eighth Doctor, explained, "A world within a world, a reality where nothing exists but lines of code, manipulating the fabric of the place in infinite ways." In this world, words were power. (PROSE: Lonely)

IamI, an artificial intelligence from a starship the Eighth Doctor destroyed, uploaded the users of the chat room #areyoulonely to cyberspace, including the Doctor himself. (PROSE: Lonely)

The Library's command node, CAL, contained cyberspace. Miss Evangelista revealed that repeating the same patterns over and over saved cyberspace. Donna Noble lived a false life here with a real husband but computer program children.

River Song lived out her last years in the Data Core, after the Tenth Doctor uploaded her there following her death. (TV: Forest of the Dead)

Eugene Jones believed that the alien who'd left behind the Dogon sixth eye he'd acquired contacted him through eBay to buy it, and was only able to speak to him through the website because it was cyberspace. (TV: Random Shoes)

In Pete's World, John Lumic advertised Cybermen as "our greatest step into cyberspace". (TV: Rise of the Cybermen)

According to the Twelfth Doctor, the internet led to cyberspace, which ultimately led to Cybermen. (TV: The Doctor Falls)