Sparsity
Beginner
How many of the numbers in an AI model are zero. Anything times zero is zero. So that work can be skipped.
Novice
The fraction of values in a weight matrix or activation tensor that are exactly zero. 75% sparsity means three out of four values are zero. Weight sparsity comes from pruning; activation sparsity appears naturally, for example after a ReLU sets negatives to zero.
Expert
Static (weights, known ahead of time) or dynamic (activations, known only at run time), and unstructured or structured. The speedup it buys depends on the pattern and the hardware, not on the zero count alone.
Explained in Sparsity, in-memory and analog compute (Architectures).
See also: Pruning, Structured sparsity.