R90 is a designation that can refer to various things, but it is often associated with the BMW R90, a classic motorcycle model produced in the 1970s. Known for its powerful engine and distinctive design, the R90 became popular among motorcycle enthusiasts for its performance and reliability. In addition to motorcycles, R90 can also refer to specific regulations or standards in different fields, such as R90 regulations in environmental science. These standards often focus on safety and efficiency, ensuring that products or practices meet certain criteria to protect public health and the environment.