That is just another name for cam timing. Both cams should be in time when the crossbow is either in the uncocked position or the cocked position. In the uncocked position, look down from above a cam where the cable crosses. Look at the other cam in the same area. If the cams are in time these reference points should match.I see the term cam synchronization listed as a price adder with some crossbows. Is this really a benefit with a new crossbow purchase? I assume the main benefit is perceived improved accuracy?
One can do the same with the crossbow cocked. The reference spot will be in a different position, but both should match.
One can use a hole in the cam with reference to the limb. I personally prefer the cable method. Once the cams are in time, I mark the cam directly below where the cable crosses with either white out or a permanent marker. When ever I go to shoot the crossbow or while shooting I can check these to see if a cable or the bow string has stretched.
Having the cams in time and the bow cocked even (center serving of the bow string properly centered) the arrow should come out straight. Using a rope cocker, sometimes as one nears the fully cocked position, one may pull a bit more on one side. This will off set the center of the bow string. To correct this, mark the bow string on each side of the rail-stock with white out when the crossbow is uncocked. Cocking the crossbow, these marks should be equidistant from the center of the rail where the arrow lies.
All the best.