stock in which there is little investor interest but that has significant potential to gain in price once its attractions are recognized. Antithesis of high flyer. Bloomberg Financial Dictionary
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a share or a product that is not successful immediately, but then suddenly starts to sell well or be successful:
• The movie turned out to be a sleeper.
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sleeper UK US /ˈsliːpər/ noun [C] (also sleeper hit) MARKETING
► a product, film, book, etc. that becomes a sudden success, after a period of not being successful at all: »
The movie cost only $400,000 to make, and then blew up into a $39 million sleeper.
»Her book has been the big sleeper hit of the literary scene.
Financial and business terms. 2012.