The red pill and its opposite, the blue pill, are pop culture symbols representing the choice between embracing the sometimes painful truth of reality (red pill) and the blissful ignorance of illusion (blue pill).
The terms, popularized in science fiction culture, derive from the 1999 film The Matrix. In the movie, the main character Neo is offered the choice between a red pill and a blue pill. The blue pill would allow him to remain in the fabricated reality of the Matrix, therefore living the "illusion of ignorance", while the red pill would lead to his escape from the Matrix and into the real world, therefore living the "truth of reality".
As narrated, the blue pill will allow the subject to remain in the fabricated reality of the Matrix, and the red pill serves as a "location device" to locate the subject's body in the real world and to prepare him to be "unplugged" from the Matrix. Once a person makes his/her choice, it is irrevocable. "Bluepills" are people who have either elected to remain in the Matrix or have not yet been offered the choice, while "redpills" have chosen to disconnect.
Which one will you choose?