Block — one rank-one term, one multiplication

Block — a rank-one tensor u ∘ v ∘ w laid over the multiplication tensor. Spanish: bloque.

(a₁₁ + a₂₂)(b₁₁ + b₂₂) = (1 + 4)(5 + 8) = 65 is two additions and one multiplication, and it bundles four products. On the tensor it is the block with u = v = w = (1, 0, 0, 1): it covers 2 × 2 × 2 = 8 cells, two of which the tensor wants and six of which are damage that something later has to undo.

Read as an instruction: add up entries of A with weights u, add up entries of B with weights v, multiply the two sums, add the result into C with weights w. One block, one multiplication, however many cells it covers.