Something that's the latest is the newest, most recent example of that thing. For example, some people always need to have the latest cellphone model, while you're perfectly happy with the one that came out three years ago.
You can listen to a singer's latest single, or read a novelist's latest book — the ones most recently written and released. The adjective latest can also describe the very most fashionable thing, like the latest hairstyle or the latest men's suit design. "The latest" is also sometimes used to mean "the news," so you could say, "Hey, have you all heard the latest on the flood at school?"