How does YouTube define impressions, impressions CTR, RPM vs CPM, and where are impressions counted?

YouTube Help (captured 2026-10-23): an impression counts when a thumbnail is shown for more than 1 second with at least 50% visible, only on YouTube surfaces (not external sites/embeds, end screens etc.); impressions CTR is computed only from views that came from counted impressions, so views/impressions will not equal CTR; YouTube states half of channels/videos fall between 2% and 10% CTR. RPM = total revenue after YouTube's share per 1,000 views, including memberships, Premium, Super Chat and Super Stickers, and the page says RPM is calculated per 1,000 engaged views for Shorts and all views for long-form videos; CPM = advertiser cost per 1,000 ad impressions before revenue share, so RPM is lower (after share and including unmonetized views). New viewers = first time watching the channel in the period; returning = watched before. A standalone "unique viewers" definition page was not retrieved in this batch (answer/9314419 and 9314422 returned a generic shell): gap. Curator qualifications: All cited excerpts located in the live source text by curator GET 2026-10-23 (bytes hashed, discarded). H4 CTR sentence is split by a link ('counted impressions'); prefix match plus link text confirmed. Discovery's note that the RPM page is internally inconsistent is a misreading: the page says RPM is calculated per 1,000 engaged views and states 'For Shorts, it includes all engaged views. For Videos, it includes all views.' (curator re-read 2026-10-23). Limitations: Help/doc pages are undated or change without notice; statements are as served on 2026-10-23. "Engaged views" basis for RPM vs older "per 1,000 views" sentence on same page: wording internally inconsistent (line 4 vs 5). Unique viewers definition missing. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://support.google.com/youtube/answer/9314486?hl=en",
      "note": "line 13; line 19; line 12; lines 4-5; line 12; segments: New/Returning"
    },
    {
      "url": "https://support.google.com/youtube/answer/7628154?hl=en",
      "note": "line 13; line 19; line 12; lines 4-5; line 12; segments: New/Returning"
    },
    {
      "url": "https://support.google.com/youtube/answer/9314357?hl=en",
      "note": "line 13; line 19; line 12; lines 4-5; line 12; segments: New/Returning"
    },
    {
      "url": "https://support.google.com/youtube/answer/9314415?hl=en",
      "note": "line 13; line 19; line 12; lines 4-5; line 12; segments: New/Returning"
    }
  ]
}