The undecorated stiff paper covers of an unbound book, manuscript, galley or uncorrected proof. Most often improperly used to refer to the decorated covers of a trade or mass market paperback book. Paperback books should be described as "PB" or "PAPERBACK" - not "in wrappers".
In data mining and treatment learning, wrappers were used by Ron Kohavi and George John. Their idea was to wrap their treatments learners in a preprocessor that would search to make subsets from the current set of attributes.
An arrangement whereby an investment (usually a fund) is sold as an adjunct to a life insurance policy. Fund investors can shelter both capital gains and investment income from tax by making use of the wrappers available.