What do you guys mean by face blindness? Do they not recognize people they have seen before?

The author of the article says he seems to have a "hash table" in his head and doesn't have a big problem recognizing people. It was one of the things that stood out for me.

I have a hard time with names. Not so much faces. I have acquaintances I've known for years that I can tell you a lot about except their name. I will notice we have the same waiter we had two weeks ago, but not remember his name when he only told us it 30 minutes ago.