In the sticker system used by Brawl, some attacks are coded as being Specials: Indirect. Generally this indicates that an attack is a projectile or is similarily long-ranged and not involving hand-to-hand contact; despite the name, they do not have to be part of a special move.
The main effect of indirect attacks is that most enemies in The Subspace Emissary resist them to a small degree. This is presumed to encourage close-range combat as opposed to camping and turtling to defeat enemies in the mode. The only enemies to not resist them are Floows and the bosses Master Hand, Crazy Hand, Porky, Meta Ridley, and Tabuu. Indirect attacks also affect certain items: Uniras are not moved or dislodged by indirect attacks, and Metal Boxes do not activate when struck by one.
List of Specials: Indirect attacks by characters
List of Specials: Indirect attacks by items
All items, with the exception of battering items when swung and the Screw Attack, are Special: Indirect.