In telecommunications, 2VSB is an abbreviation for 2-level vestigial sideband modulation, a transmission method capable of transmitting one bit (21=2) at a time.
Other faster but less rugged forms include 4VSB, 8VSB, and 16VSB.
References VSB-dependent automatic gain control, Jung Sig Jun et al., U.S. patent no. 6,281,945. Accessed on line 12 January 2008.