Closed bolt - Ball is loaded, bolt closes and stays in this resting position until fired.
Open bolt - Ball is loaded, bolt stays open and stays in this resting position until fired, in which the bolt moves forward into a closed bolt position.
In both situations, the bolt will end up being in a closed position before firing. When you're firing repeatedly, particularly at high speeds... open bolt and closed bolt are mechanically doing the same thing.
Closed bolt gun: Autococker
Open bolt gun: Automag
There is no ROF/accuracy/range advantage to either... with firearms there is a difference because closed bolt rifles allow for tighter tolerances... but this is not the case with a paintball marker (a popular myth that won't die).
Blow back: Air blows bolt back to recock bolt/spring.
Blow Forward: Air blows bolt forward and spring returns bolt.
Example blow back gun: Spyder, and Spyder derivatives including the Angel and Intimidator (which use pneumatics in place of the spring).
Example blow forward gun: Automag family, various others that I can't remember.