Shards
UO is split up into different servers called Shards that are located all over the world. Players usually select a shard in or closest to their time zone. This helps reduce Latency, which can cause Lag.
Shards
There are currently 26 production shards. Production shards are where "normal" gameplay occurs.
Other Shards
These shards have either closed, were one time events, or had other purposes.