CPL's Book a Week Challenge discussion

We see it all the time on book reviews - "A perfect summer read; Excellent book to read on the beach; Best summer book; etc."

But what do those even mean? What makes a book a "vacation/summer read?" And is this question not answerable due to the number of different tastes and genres (though the publishing industry obviously thinks its answerable)?

weirdly enough, I tend to take a lot of nonfiction books on vacation. With fiction, especially suspense fiction--things that might normally fit the definition of beach reads--I get so interested I can't put them down. With nonfiction, I find I can step away if needed to do vacation-type things.

For me the perfect vacation read is the time to go thru my book shelf and read the books I have trying to read for last couple of years. On that note I am dusting off some of those books and bringing them with me on my vacation.