The best example of a domain-specific language (DSL) from the options provided is "shape."
A domain-specific language is designed to handle a specific set of tasks or problems within a particular area or domain, and "shape" suggests a category commonly associated with graphical representation or geometric processing, making it suitable as a DSL example compared to the other options. "Equilateral" also signifies a specific type of shape (like an equilateral triangle), but it is more specific than the broader concept of "shape."
If the context allows for further distinction, clarify whether you are looking for the most general language or the most specific to a use case.