https://wccftech.com/channels-start-appearing-for-windows-10-insiders/

Earlier in the month, Microsoft announced moving away from what it called called "rings" to channels for its Windows Insider Program to align the term across its ecosystem. Replacing Windows 10 Fast, Slow, and Release Preview rings are Dev Channel, Beta Channel, and the Release Preview Channel.

While everything largely remains the same, the Windows maker had said that new test builds will be matched with a specific Windows 10 version when these builds land in the Beta Channel. Up until now, this happened in the Fast ring aka Dev Channel. But now, Dev Channel rings aren't tied to any specific version and can land in any of the future feature updates of the operating system.