Contingent convertible capital
From ACT Wiki
Contingent convertible capital is made up of hybrid capital securities that, through a conversion mechanism, provide addtional capital available to absorb losses when the capital of the issuing institution falls below a certain level. They are generally used by banks in meeting regulatory capital requirements.
"Contingent convertible capital securities" is frequently and conveniently abbreviated to "CoCos".
The BIS's quarterly report of September 2013 has a useful primer on CoCos.