A vacuum fluctuation occours when "probability smudges" in space-time somehow spontaniously become reality. The effects of this are to instantly create two particles from nowhere; a Proton and an anti-Proton for instance. These two particles fly outwards from a single point for a mere instant, then are drawn back towards each other, and finally collide, totally anihilating each other. Unlike normal matter/anti-matter collisions, no energy is created in the form of gluons, as an anti-gluon is created with the particles.
 

 S              Particle Path
 P             +    +     +
 A          +                 +
 C        +                      +
 E      +     anti-gluon path      +
        ***************************** point of collison
        -                          -
          -                      -
             -                 -
                 -    -    -
              Anti-particle Path

                      TIME

The space-time diagram above shows the paths of the molecules and the anti-gluon.

Some theorists belive, and I personally think this idea deserves much merit, that the whole unverse was created through one massive vacuum fluctuation, which is in concordance with the "big bang" theory, as all matter would have come from a single point. The main drawback of this theory is that there is no sign of all the anti-particles and anti-gluons which should be floating about.