Is there a concise description of what ‘special’ damage is?

Hello RPG Stack this may be somewhat a worthless question as I’ve looked diligently without success. I don’t believe the information is physically present but I thought I’d give it a shot. In my games things have temporarily side stepped in to the sword and planet genre (lol don’t ask) and I find myself in need of modelling a famous character from the genre. I was looking at page 146 of the Dungeon Master’s Guide under the Futuristic Weapons heading as it states:

‘Futuristic weapons are like other ranged projectile weapons, though the type of damage they deal is special.’

My question, is there anywhere in D&D 3.5 rules that defines concisely what special damage is?