If Microsoft decided to sell mobile phones under the Xbox brand (which it uses for its gaming systems), this would be an example of a line extension.
This is a brand extension, not a line extension. A brand extension is the use of the same brand name in a different product line. Phones and gaming systems are different product lines.

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Quizplus · Accepted Answer

This would be an example of a brand extension, as it involves using the Xbox brand name in a different product category (mobile phones) rather than extending an existing product line.

If Microsoft Decided to Sell Mobile Phones Under the Xbox