A range of radio frequencies between 3.7 GHz and 4.2 GHz (as defined in the US, or 4 – 8 GHz internationally). Before 2021, this was used primarily by commercial satellites, offering TV and data services.
Between 2019 and 2023, the US FCC orchestrated a process to re-allocate the lower portion of this band (3.7 – 4.0 GHz) for 5G mobile networks.
This is also known as "mid-band" spectrum, which offers a good balance of coverage and fast data speeds for improved 5G service.
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.
See: Band 77