Original: A "second wave" arose in the early 1990s, spearheaded by Norwegian bands such as Mayhem, Burzum, Darkthrone, Immortal and Emperor.
Simplified: Second wave is the most popular wave of black metal and it started in the early 1990s. It started from Norway and includes bands such as Darkthrone, Enslaved, Burzum, Satyricon, Mayhem, Gorgoroth, Immortal, and Emperor.