Historically, SA stood for "Sturmabteilung" which referred to the stormtroopers or brownshirts, the Nazi Party's paramilitary wing, which in 1931-1933 (and again later) beat up opponents of the Nazis in the streets. Originally, the SS was a section of the SA but became fully autonomous in 1934. Since 1945 the abbreviation has been avoided in Germany in non-historical contexts.