An "undiscovered planet" refers to a planet that has not yet been found or explored by humans. It means that it has not been seen, studied, or known about before. Full definition
Though this planet is very un-habitable for life as we know it (as it's very close to its star), there could be other undiscovered planets in the system. (seeker.com)
And no, none of this has nothing to do with Nibiru, a pseudoscientific belief in a large undiscovered planet which would collide with Earth, based on teachings by Zechariah Sitchin. (planetaria.ca)
And no, none of this has to do with Nibiru, a pseudoscientific belief in a large undiscovered planet which would collide with Earth, based on teachings by Zechariah Sitchin. (americaspace.com)