A radio frequency band near 800 MHz. In the US, Sprint uses it for CDMA (and LTE) service.
It was previously used for iDEN service, and was known as the ESMR band.
See: ESMR
The "BC10" designation is generally used only when discussing CDMA service. Other common band classes include BC0 (850 MHz) and BC1 (1900 MHz).
For LTE service, band numbers are used instead of "band classes". Band 27 covers the same frequencies as BC10. However Sprint uses band 26 for its 800 MHz LTE service, which is a larger band definition that includes all of the frequencies of both BC10 (band 27) and BC0 (band 5).
See: Band 26
Phone Scoop refers to CDMA service in BC10 as "CDMA 800".
See: CDMA 800