Meekrob is the planet to which Invader Tenn was assigned. The dominant species native to the planet are highly intelligent beings of pure energy, which would make it hard for Tenn and her SIR Unit to disguise themselves. The Meekrob are sworn enemies of the Irken Empire.
In the episode "Megadoomer", Tenn was supposed to receive a Megadoomer Combat Stealth Mech as a gift from her leaders, but - thanks to a rebellious worker on the Conveyor Belt Planet switching the labels - instead received a package of deadly malfunctioning SIR Units, which were meant for Zim; as a result, Zim ended up receiving the Megadoomer, while Tenn got the psychotic robots, which promptly began to destroy her base.
The Meekrob made their first and only physical appearance in "Dib's Wonderful Life of Doom". However, these were not real Meekrob, but illusions created by Zim, and while this is may be their true appearance, Zim's track record with factual accuracy provides an element of doubt.
It is also unknown how the planet Meekrob looks like from space, though the terrain appears to be rocky and barren.
Had the series been completed, there would have been a two part special in which the Meekrob discover Tenn. This would have resulted in an all out war with the Irkens on their planet, The Resisty would have assisted them, and Dib, after saving their planet, would've been named the Ambassador of Meekrob.