DesignScript
Short answer
The textual scripting language Dynamo's code blocks use — a stricter cousin of Python with stronger type safety.
DesignScript is the textual language used inside Dynamo Code Blocks. It looks like a constrained scripting language: variables, list comprehensions, and direct calls to any Dynamo node by its full name (e.g. Point.ByCoordinates(0,0,0)). DesignScript is faster to author for one-off transforms than wiring 10 nodes, and Dynamo graphs heavily mix Code Blocks with visual nodes.