dynamic languages are languages who perform many central operations, like type checking at run-time rather than at compile type. They facilitate changing the object system, and a host of other things too long for the post. (https://en.wikipedia.org/wiki/Dynamic_programming_language)

I was playing a little lose with language because the OP was talking about interpreted and compiled languages, and not all interpreted languages are necessarily dynamic, but in practise the fault lines are about the same.