16VSB is an acronym for 16-level vestigial sideband modulation, capable of transmitting four bits (24=16) at a time.
16VSB is capable of twice the data capacity of 8VSB; 8VSB delivers 19.34 Mb/S (Mega Bits Per Second), 16VSB delivers 38.68 Mb/S.
While 8VSB is the FCC ATSC (USA) digital broadcast modulation format, 16VSB was planned for cable distribution. 16VSB is about twice as susceptable to noise, therefore less suitable than 8VSB for broadcast, but well suited to the SNR of fiber/cable distribution, allowing twice as much programming in a 6MHz band channel.
However, as of today (Jan 2004) it looks like cable will not carry VSB but will instead carry any DTV programming via 256QAM, the standard modulation method for digital cable in the US.