Euphrates-class colony ship
From Halopedia, the Halo wiki
The Euphrates-class colony support vessel is a kind of colony ship employed by humanity. Hundreds of Euphrates-class vessels were constructed in orbit over Luna alongside Phoenix-class colony ships and the Odyssey to depart on a massive effort to colonise new worlds - a process known as the Domus Diaspora. Euphrates-class ships are employed for the purposes of terraforming, with the small ships used for a wide range of functions such as atmospheric processing, water purification and introducing Earth flora to the new world.
- Halo Encyclopedia (2022 edition), page 116