Question: "What crossed over?"  Context: "Since the mid-2000s, the mainstreaming of bands like Wilco and Feist have pushed indie rock into the adult contemporary conversation. In the early 2010s, indie musicians like Imagine Dragons, Mumford & Sons, Of Monsters & Men, The Lumineers and Ed Sheeran also had indie songs that crossed over to the adult contemporary charts."  Answer:
indie songs