Imprinting is one of the many abilities conferred by the Player Pin. It allows Players to insert memes into people's thoughts in the Realground. These people usually react to imprinting as a burst of inspiration, which will generally influence them to do what the Player wanted in order to clear a mission.
In the game, imprinting can only be done when one person starts to think about something related to solving the mission, and the Player has at least one meme to hand. This may not always be the correct meme, as the Player can encounter several, but when it is, it will advance the plot.