The concepts come with the idea of a persistent game map, which is online 23/7 and never wipes.

When UO came out, it had to deal with a large game world that nevertheless would be too small to reasonably hold a number of players that represented financial success. So the game world was duplicated on multiple servers running the same map. A player on Atlantic server could have no interaction with a player on Chesapeake server. If you wanted to play together you needed to make characters on the same server. In-game this was reflected in cosmological lore about the world being some kind of crystal that was shattered into shards. This jargon spread, to some extent, to be a generic terminology in MMORPGs.

I believe UO launched with only three shards, and added a couple dozen at the height of its popularity.

Eve is notoriously a single-shard game, with the player count being accommodated in other ways as the map grows larger and more organized play is added patch to patch, and the actual play changing notably from the era of 5,000 simultaneous online to the era of 50,000 simultaneous online.

Even without deep skill-stat specialization, when your alliance has 500 people it lends itself strongly to role specialization, because an alliance of 500 people is an organization of 500 people, who find different things fun in different contexts, and whose operations have every category of need you would find in a small nation state, from diplomacy to collective resource allocation to logistics to surveying to espionage to military service, recruiting, communications, practice and command.

Eve has every player on the same global system, and "shards" only by running the code for a particular system on a particular server. As a result, if you're in Eve Online every other player has some influence on you however minute.