What is the Difference Between 4K and UltraHD?

Ultra high definition suddenly entered our lives. So, is there any difference between "4K" and "UltraHD"?

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What Is 4K (Ultra HD)?

What is 4K- High-definition Video Digital Transmission Protocol

From 4K to UHD to 1080p: What You Should Know About TV Resolutions

Ultra HD vs. 4K TVs: What's the Difference?

4K UHD TV vs. 1080p HDTV - Side by Side Comparison

4K vs 8K: What's the Difference?

Ultra HD vs. 4K TVs: What's the Difference?

Ultra-HD / 4K resolution

Key Differences Between 4K and UHD Resolutions

4K vs. UHD: What's the Difference?