Operator cotype describes how a bounded operator between Banach spaces acts on finite random sums
of vectors. The two principal versions are Gaussian
cotype, which uses independent standard Gaussian coefficients, and Rademacher
cotype, which uses independent random signs. For 
, each version is quantified by the least constant comparing
the 
-sum
of the image norms with the expected norm of the corresponding random sum.
For an identity operator, operator cotype gives the corresponding cotype property of the underlying Banach space. Comparing the Gaussian and Rademacher constants together with a related summing norm gives Talagrand's operator cotype problem.
