From Halopedia, the Halo wiki
OUROBOROS involved several pillars, one of which was the research and development that resulted in the construction of UNSC Infinity. Conceived of as a hedge against extinction, Infinity was originally intended to be a mobile colony to carry survivors to distant stars in the event of social collapse triggered by the ongoing Insurrection, the threat of the Covenant, or other catastrophe. The sensitive nature of these plans and their potential impact on United Nations Space Command morale meant Infinity was built in strict secrecy. Many of those who supported the plan to use Infinity as a last resort lifeboat were unaware when the ship eventually was repurposed for a military role in the UNSC Navy.
The Ouroboros is an ancient symbol depicting a serpent or dragon eating its own tail. It represents the infinite cycle of nature's endless creation and destruction as well as life and death.