Something resurgent comes back to life or is reinvigorated. An old song's popularity might be resurgent after it's featured on the soundtrack of a popular new movie.
When things fall out of favor or stop being active and then experience a burst of energy or interest, they're resurgent. After a period of very conservative political control, resurgent liberal beliefs could lead to a progressive president being elected. And if people get bored with new technology and gadgets, there may be a resurgent interest in hardcover books and Polaroid cameras. In Latin, resurgere means "rise again."