What is a "wafer pin tumbler" lock

[candado3]

I have seen padlocks referred to as "pin tumbler", "wafer tumbler", "wafer" but have not seen them referred to as "wafer pin tumbler" until I was browsing the antique-padlocks.com webpage where I came across the term a few times.
Can anyone explain to me what a "wafer pin tumbler" padlock is?
Thanks.

[Josephus]

Tumblers are parts of the lock that interface with the working surface of keys. Wafer pin tumblers, like the more common "pin and tumbler" locks are simply an ignorance of terms.