"One of the important design goals for Canon’s engineers in developing the new 61-point High Density Reticular AF system in the EOS 5D Mark III and EOS-1D X was to truly optimize the performance of each point on the autofocus sensor. It’s easy to toss around terms, but if a photographer is not clear on what they mean, they may miss out on a lot more than a marketing pitch. Knowing the characteristics of the AF array in these cameras puts the photographer in the position to get the most out of the AF system.
Cross-type AF points: what are they?
Certainly a fair question. And all the more so, because it's not something the photographer can see just looking through the viewfinder. Perhaps the easiest way to answer it is to take a trip down memory lane in AF SLR design..."
Read the information-packed article on the Canon Digital Learning Center. (thanks Stuart)