Coated strings have become more and more popular over the last decade or so. Some of the best acoustic guitar strings have a coating around the string that helps prevent dirt and sweat from getting into the grooves, making them sound like new strings for longer.
Coated strings are usually more expensive, but you won’t have to replace them as regularly, because they retain that fresh, bright sound for a longer period. Some coated strings have a slightly different feel, but if you’ve never tried them before then they’re worth investigating.