Registered trademark Pigweed.
Google has registered the trademark for the new operating system. A document in the United States Patent and Trademark Office (USPTO) was highlighted by users of the Reddit social media news site.
Google has acquired the rights to the Pigweed brand. As stated in the description, the Pigweed brand belongs to the category of computer operating systems.

Further details are not yet available in official sources. However, this is not the first mention of the name Pigweed. Last November, the name Pigweed was seen in another Google’s code, the Fuchsia operating system, which is still in its infancy. The second mention of Pigweed was found in the Google Chromium repository.
For now, we can only guess and wait for Google to make official announcements about Pigweed.
Note that the Android brand was registered five days before the OS debuted in 2007, but the Chromebook was registered months before the first Chromebooks began shipping in 2011. Fuchsia has been a registered brand for two years, but has not yet been released by the company.