Damage is stuff you absorb and it decreases you're health over time. Different things hurt you more then others. Like bullets from a Chinese Assault Rifle hurt more then a Lead Pipe to the leg. It also depends on what the weapon is, what kind it is, how good the user is, and how much resistance the receiver has. Also stealth kills do more damage, and it depends where you hit them, and what type of protection they have on.
Related ThreadsNew Vegas to have Damage Threshold instead of Damage Resistance - last post by @ Sep 29, 2010
colour damaged - last post by @ Dec 15, 2012
Weapon Damage Glitches - last post by @ Feb 28, 2010
The bullets damage - last post by @ Dec 20, 2008
Damaged Armour - last post by @ Jul 14, 2009