Binary planet
Binary planets were a pair of planets that revolved around their shared center of mass while also sharing an orbit around their primary.

The Chin'toka system's second and third planets were a binary pair. They themselves had at least two moons. ()

Appendices

See also
Binary star

Background information 
While the term "binary planet" is not used in the episode, the two planets in "Tears of the Prophets" are referred to as such multiple times in the script. 

Various background sources have described the large companion often seen in the skies of  as being a co-orbiting sister planet called  . Examples include The Worlds of the Federation (p. 18), which describes their relationship as , and Star Trek: Star Charts (p.58).

Although Romulus and Remus are referred to as sister planets and appear remarkably close to each other, a computer graphic seen in  shows them to have their own distinct orbits around the Romulan sun, meaning that they are not binary planets.

According to StarTrek.com, Tyrus VIIA was "one of a double planet" with Tyrus VII.

External link 
 
Celestial objects