Although you cannot see it in the photo, these switches have two rows of terminals - the second is behind the visible row.
Looking at the photo, if you look at half of the visible terminals, this is essentially a mechanism that switches one common terminal to connect to one of the five other terminals for each respective switch position. This switch can be considered to be four of these mechanisms working in unison.
These switches allow access to an array of wiring schemes that are not possible with standard switches. Standard 5 way blade switches have three terminals (and one common) in each side of the switch. They work by switching between the terminals in each position, with the second and fourth positions bridging the first and third, and third and fifth position terminals respectively. Having unique terminals means that the second and fourth positions don't necessarily have to be a combination of the positions to either side of them (unless it's wired up to do so). This gives much more freedom to allow you to wire the switch up to do completely different things in each position!