Alchemy.Events.on_guild_update

You're seeing just the macro on_guild_update, go back to Alchemy.Events module for more information.
Link to this macro

on_guild_update(func)

(macro)

Registers a handle triggering whenever a guild gets updated.

args : Alchemy.Guild.t

A guild gets updated for various reasons, be it a member or role edition, or something else. The guild updated with this new info will be sent to the hook.