A Demo is usually a single level, or part of a level, that should demonstrate what the game will be like.
Game Developers mostly release these demos a few weeks before the full game is released. A demo serves as promotional and preview material and for the developer and helps the PC gamer to find out if his/her hardware is compatible.
Here's a (partial) list of the Tomb Raider Levels, that served as demo:
- Library Demo (not found in the actual game)
You can find a walkthrough here: http://www.tombraidergirl.com/tr7/demo.php
Tomb Raider (2013)
Tomb Raider (2013) does not have a downloadable demo. There were publicly playable levels at conventions:
- E3 2011 demo showing the Scavenger's Den Demo, also playable at Community Events around the globe
- E3 2012 demo, called the Hunting demo, also playable at Community Events around the globe and at Gamescom 2012.
Rise of the Tomb Raider
Rise of the Tomb Raider also features two gameplay demos shown at conventions and fairs beforehand.
- E3 2015 Siberian Wilderness Demo
- E3 2015 Syria Demo