Convertible Subordinate Note
A short-term debt security (note), that can be changed into common stock (convertible) and ranks below other loans (subordinate).
Investopedia Commentary
Don't let all the words in this term intimidate you. Break up the term and it's easy to see this is just a short term bond that has the conditions of being 1) convertible to stock, and 2) subordinate to other debt.
This is a common type of debt that companies issue.
Related Links
Convertible Bonds: An Introduction
See also: Bond, Convertibles, Note, Subordinate Debt