Interactive TV Dictionary and Business Index
The Definition of 2-Screen Interactive TV
2-Screen Interactive TV – (May be known as  2-Screen TV, Two-screen Interactive TV, PC-delivered two-screen Interactive TV applications, 2-screen Synchronized Interactive TV, SyncTV, Synchronized TV, PC-Synchronous Enhancements, Two-screen TV,  Split Screen Programming, Split-screen TV, Synchronized Interactive TV {Application}, Telewebbing, 2-screen Interactive Applications, Broadcast-synchronized Interactive TV, 2-screen Internet Application.) - 2-screen Interactive TV is giving way to Single-screen Interactive TV. However it's still a major form of Enhanced and Interactive Television.

(1) (This is the primary definition) - The most dominate example of 2-screen TV is when a TV program asks you to go to their Web site for more information.  2-screen Interactive TV was developed for use as so many television systems lack a built-in return path. With 2-screen Interactive TV, someone watching TV can separately use a computer, mobile or another device to interact with that TV program, the network operator, the program's viewers and/or advertisers. See Interactive TV Using Mobile Devices.

(2) Split-screen TV, Split Screen Programming - When the television programming and return path are presented in separate frames on the TV screen.

Some Related Definitions:

Authoring Tools - (Interactive TV)
Back Channel
PC-Synchronous Enhancements
Single-screen  Interactive TV
Synchronous Enhancements
Synchronous Programming
Synchronized TV Developer