Partial sum
Beginner
A running total that isn’t finished yet. More products still have to be added to it.
Novice
An output value part-way through its accumulation: the sum of some, but not all, of the products that make it up.
Expert
Often abbreviated psum. Partial sums are wider than the operands (for example 32-bit sums of 8-bit products), so moving them costs more wire and energy than moving inputs; where they live is a key dataflow choice.
Explained in Systolic arrays (Architectures).
See also: Accumulator, Output-stationary (OS).