Because I had to look it up:
SPSC = Single Producer Single Consumer
MPMC = Multiple Producer Multiple Consumer
(I'll let you deduce the other abbreviations)
S = Single
M = Multi
---
C = Consumer
P = Producer
They could have named that 1:1, 1:n, n:m, n:1, but deemed it too old and unfashionable.
S = Single
M = Multi
---
C = Consumer
P = Producer