by Dave Young @ element14.com:
A ULP (User Language Program) is a feature designed into EAGLE to allow users to generate their own processes to automate tasks that would otherwise be tedious and time consuming. While most users know that this functionality exists, very few want to write their own script. A casual user would have to dump far more time learning the system and designing/testing their code than just completing the task at hand.
EAGLE ULPs Every User Should Know – [Link]