A range of radio frequencies between 3 GHz and 8 GHz. This includes the 5 GHz unlicensed band used for Wi-Fi, as well as the 3.7 – 6.4 GHz band that has long been used by commercial satellites.
This is also known as "mid-band" spectrum, which offers a good balance of coverage and fast data speeds for improved 5G service.
In 2019–2023, the US FCC is conducting a process to re-allocate parts of this band for ground-based mobile cellular networks, which are expected to deploy 5G technology in this newly-available radio spectrum. The part being re-allocated for 5G in the US is 3.45 – 3.98 GHz. The FCC will hold a public auction of new licenses in this band for wireless carriers, and use that money to compensate incumbent users, including satellite operators. Some of those operators will need to launch new satellites to make these frequencies fully available.
In order to support C-Band networks in the US, phones need to support 5G in band 77, often referred to as NR 77 or n77.