There are two meanings for this word:
There is a menu option, on the Main Menu for each game, that presents an overview of what has happened in the game over the past three seasons. This includes major activities such as battles, sieges, marriages, births and deaths, etc.
Then there are the people who help you out, called Heralds. This last crew are very similar to the medieval Heralds, who tried to keep score and carry messages to the warring factions. There are several levels of Heralds on the HYW staff. The newest are Apprentices, followed by Journeymen and then Master Heralds. Assistant Sysops are Master Heralds who also run their own games under the supervision of their Team Leader. At the top of the Ladder are the Sysops, who have teams of Heralds they work with to ensure that their games run smoothly.