The term "Damage Spread" is thrown around, specifically in regards to "vanilla" servers in Team Fortress 2. What does this term mean, and how does it relate to server settings and gameplay?
Damage spread refers to the fact that a weapon has a spread, or range, of damage that it can deal on any given hit. By default, weapons generally have a +/-10% damage spread.
So if a weapon has 100 base damage, it might do as little as 90 (10% less than base) or as much as 110 damage (10% more than base) on hit. This amount of damage dealt is simply a random value from within the "spread".
Originally, the spread was +/-25%, but Valve eventually reduced it to only +/-10%.
Note that this isn't the only thing that affects weapon damage, there is also a damage falloff based on range for most weapons (they do less damage at greater distance).
Some servers disable damage spread because they think it makes the game more "skill-based" and more fair, since damage dealt is more consistent. This is similar to the argument used for disabling critical hits.