Perceptual barrier

Perceptual barriers were a method of hiding things.

The Time Lords used perceptual barrier to hide memories. When the person tried to think about the topic the memories became vaguer, but these memories could randomly crop up if the person thought about something else. The Time Lords put a perceptual barrier inside Lucie Miller's mind, stopping her from remembering why she had been taken to the Eighth Doctor for safekeeping. (BFA: Blood of the Daleks)

The Viyrans used a perceptual barrier to hide Lower Downham, making it seem to disappear from both existence and from people's memories. (DWS: No One Died)