Tarella was an inhabited planet. Classified as M-class, this was the homeworld for a warp-capable humanoid species, the Tarellians. It was very similar to Earth.
A civil war between the planet's two main land masses led to the destruction of the Tarellian civilization after biological weapons were deployed. A few Tarellians managed to escape the planet in ships. (TNG: "Haven")
This planet was only mentioned in dialogue.
According to the script of the episode, Tarella was the second of six planets in its star system. [1]