Answer:
Sonnet 18 is part of a series of sonnets in which William Shakespeare refers to love making comparisons with tangible issues in the world, in this case, with summer: he refers to his love, presumably also a man, comparing him with summer, making reference to the beauty of said season and its likeness to his loved one, even considering him as more beautiful than the season itself, since the latter is temporary, while the beauty of his loved one is permanent and immutable.