Memories were the mental record of a lifeform's past experiences.
A man is the sum of his memories, you know. A Time Lord even more so.
Clara Oswald read the Doctor's name in The History of the Time War. When that timeline was later averted, however, she had no memory of it. (TV: Journey to the Centre of the TARDIS) The telepathic circuits of a dead TARDIS retrieved some of those lost memories. (TV: The Name of the Doctor)
Retcon was a drug used by Torchwood to remove memories of the organisation and/or alien encounters from witnesses. (TV: Everything Changes, Adam, They Keep Killing Suzie, Meat, Something Borrowed, COMIC: Shrouded) The drug was also used by other individuals and organisations, notably the mayor of the trap street, Ashildr. (TV: Face the Raven)
In order to prevent Clara Oswald from dying, the Twelfth Doctor tried to use a neural block to erase himself from her memories. Upon learning of his plan, Clara reversed the polarity of the device and the Doctor lost his memories of her instead. (TV: Hell Bent)
After Bill Potts's encounter with a puddle of sentient oil in the form of her friend Heather, the Twelfth Doctor intended to wipe her memories of the event. Bill realised his intentions and pleaded him not to. Eventually she gave in but before he could go through with it, she told him to imagine how it would feel if someone did it to him. The Doctor, perhaps remembering how Clara Oswald distorted his own memories, reconsiders his actions and lets Bill remember. (TV: The Pilot)