Which event means "this changed"

Events are named after what backs a piece — page.*, topic.* — while /items calls all of them items. They are the same things. This page is the mapping.

Ask the API for it

GET /api/orgs/{orgId}/webhooks/events

{
  "events": ["page.created", "page.published", "page.updated", "…"],
  "catalog": [
    { "event": "page.published", "item": "page", "subscribe": true,
      "means": "A page's content changed for readers. Fires on EVERY publish, not only the first." }
  ]
}

item is the kind the same piece carries in /items. subscribe marks the events a content sync actually wants.

The short answer

A blog post, a forum thread, a changelog entry and a roadmap card are all topics. A documentation page, an FAQ answer and a careers posting are all pages.

Renames

Renaming a published page changes the address readers are sent to and publishes nothing. That used to reach no subscriber at all, so a synced copy elsewhere kept pointing at an address that only redirected. page.updated carries { pageId, from, to }.

Ordering

Deliveries are at-least-once and unordered. sequence in the body increases per organization, so a stale delivery is discardable rather than damaging, and X-Forumulate-Delivery is the key to deduplicate a repeat on.