The Cartesian product of a finite or infinite set of modules over a ring with only finitely many nonzero entries in each sequence.
External Direct Sum
See also
Cartesian Product, External Direct ProductExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "External Direct Sum." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ExternalDirectSum.html