Modern words are words for things like "car," "airplane," or "computer," that wouldn't be found in The Elder Scrolls. All other words must be able to fit into the setting.

I understand canon just not the other two

Semi-Canon words are words that are related to a Canon word. For example, "Geyol" or "Ignite" is Semi-Canon because it has a Canon word in it, "yol". Non-Canon are words that have nothing to do with any other words. They are completely made up with no correlation to Canon words at all.

• Canon: invented and aprroved of by Bethesda. Can be in-game or from Prima Games Guide (who got the list from Bethesda).
• Semi-canon: NOT from the game or Bethesda, but BASED OFF OF a canon word or concept, no matter how srongly or loosely.
• Non-Canon: has NOTHING to do with canon, even if the definition describes something in TES universe.
• Modern: Anything that is not in TES universe, but that, instead, we have concept of (like billiards). These should always technically be semi-canon.

THIS IS ALL IN THE CONTRIBUTER'S MANUAL

Thank you all