The best example of a domain-specific language (DSL) from the provided options would be "shape."
A domain-specific language is typically tailored to a specific application domain, and "shape" could refer to a DSL focused on graphic design, geometry, or similar fields. Options like "equilateral" may describe a specific type of shape but are not indicative of a language on their own, while "numerous" does not relate to a domain-specific language at all.