I heard of block harmony when I was experimenting with the dictionary in my Yamaha PSR 192 Database, and later when I went on Wikipedia.
Both of these things told me that blocks are harmonies made up of four notes.
The thing I have trouble understanding is why a C major tetrad isn't called a block. It has four notes, C, E, G, and another C. Is it because even though there are two different C's in octaves, they are still considered as one? Or, is it something else entirely?
In a block, if I played C, it might harmonise below. C4, A3, G3, and E3, which makes it sound like a C major add six. It could also harmonise above. C4, E4, G4, and A4.