An Acrostic poem is one in which the first letter of each line spells out a message. Often this will be the name of a patron, or the solution of a riddle - once Giovanni Boccaccio wrote an Acrostic that revealed an entire Sonnet.
An example of an Acrostic would be
Compiler of information User input driven Neat in its notation News is daily given Amassing our knowledge Notifies our College
The Acrostic is an ancient form and dates back to at least 1000 BC.