World contains various geographical continents and facets.
Some servers have special rulesets
Below is a list of available shards in UO.
Travel between worlds
The only known means of traveling between worlds is through the use of a rare black portal, such as the one used by Lord British at the day of his departure from the world of UO. Or the Paid Character Transfer Service offered by Electronic Arts for a fee.
Felucca & Trammel
The shards, being broken pieces of the Gem of Immortality, contain multiple facets or faces. When the Wizard Mondain was slain, his apprentice, the Enchantress Minax, escaped the Avatar by using a powerful spell that transported her to a differenct facet of the same shard. From here she planned her revenge, seeking a way to travel back to the original facet from whence she escaped and destroy both Lord British and the Avatar. She has found willing slaves in the creatures of the dark facet, which she calls Minaxia in her own honor.
She has unlocked the secret to travelling between shards, and has been using her willing followers to subject Lord British, and in fact all of Britannia, to attacks by her monstrous minions. At length, she forced Lord British to use all his available resources and powers to move his people and loyal followers to yet another facet of the shard, where the Virtues block Minax herself from attacking him directly. Unfortunately, her minions can still make the journey into Lord British's new home, but because the Virtues hold sway over the new lands, players will find themselves unable to harm each other by direct or indirect means.
--Taken from the Playguide, Ultima Online Renaissance