It usually refers to documents of title (such as bills of lading) that
are tradeable or bills of exchange etc., which are sometimes combined
into things called 'documentary credits' or 'documentary collections'
which at one time enabled world trade and made UK merchants and ports
such as Liverpool rich.
Try and find a copy of 'Uniform Rules for the Collection of Commercial
Paper'. published by the International Chamber of Commerce.
Short term i.e. less than one year unsecured bearer securities that are
issued at a discount to par by public limited companies with a full
listing on the London Stock Exchange. Commercial Paper does not pay
dividends / coupons and is redeemed at par.