Earth

Earth is the alleged location of the 13th Colony, destination of the 13th tribe of Kobol, as related in the Sacred Scrolls.

and the intended destination of the survivors from the Twelve colonies.

Commander Adama uses the legend of Earth to give his people hope following the devastating Cylon attack on the Twelve Colonies, claiming that it is no myth and that its location was a closely-guarded secret among the senior military leaders - himself included.

While she is initially sceptical - going so far as to rebuke Adama for his lies to his crew, Laura Roslin nevertheless becomes the most fervent believer in Earth. Her transition is apparently due to her use of Kamala to treat her cancer, a side-effect of the treatment seeming to be visions. For Roslin, these begin with a dream about Leoben Conoy before his is discovered hiding in the fleet (Flesh and Bone - and who first gives them a clue that they will find Earth; and they culminate with visions of the Tomb of Athena on Kobol and the Arrow of Apollo (Kobol's Last Gleaming, Part I, both of which set her at odds with Adama, and result in her arrest and removal from office on Adama's orders (Kobol's Last Gleaming, Part II).