The hyperbole 'endless beach' describes a very long stretch of beach, exaggerating its length to convey a sense of vastness and to enhance the feeling of an enjoyable summer activity.
The underlined hyperbole 'endless beach' in the sentence 'We ran for miles along an endless beach, enjoying the last day of our summer break.' is a figure of speech that emphasizes the long and seemingly unending nature of the beach. It describes a long stretch of beach that the characters were running along.
In literary terms, hyperbole is a deliberate exaggeration used to create impact or to convey strong feelings. By using the word 'endless,' the author does not mean that the beach literally has no end, but rather that it is very long and the end of it cannot easily be seen, contributing to a feeling of vastness and enhancing the sense of a prolonged and enjoyable activity within a fun summer vacation.