What does bay area thrash mean?

bay area thrash meaning in Urban Dictionary

a steel scene were only available in the early 1980s in San Francisco, CA Bay region by thrash rings like Metallica, Testament, Exodus, Heathen, Vio-Lence, and others. Devoted cult following.Also used to describe a certain style of thrash, many quickly recognizable by sped-up center areas and a grounding in traditional speed metal.