A translation of the French vers d'occasion (literally, verse of the moment or occasion) – a poem written to commemorate a specific occasion, such as Yeats' “Easter 1916” or, possibly, Donne's “Nocturnal upon St Lucy's Day”.
Editors. "Occasional Poem". The Literary Encyclopedia. First published 01 February 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=785, accessed 10 March 2014.]