Final answer:
The sentence contains an adjectival clause that provides more information about the name.
Step-by-step explanation:
The sentence 'The most popular girl's name when I was born was Ashley' contains an adjectival clause that modifies the subject 'name'. An adjectival clause functions as an adjective and provides more information about the noun it modifies. In this case, it describes the name that was popular when the speaker was born.
Learn more about Adjectival Clauses