The "Reds" were just communists. The "Whites" were anti-communists who opposed them. There was a "Red movement" and a "White movement" in Russia. Finland was part of Russia at the time. It was technically a part of Russia because it was a Grand Duchy that belonged to the Russian Tsar (though it was self-ruling). After the Tsar was overthrown, and a provisional Russian government was established, Finland was no longer "owned" by a Russian monarch, so there was no real legal basis for the Finnish-Russian union to continue. The new Russian government was overthrown by the Reds (the Bolsheviks), who had declared the right of self-determination for all their subjects, including secession from Russia. They thought their communist revolution would simply spread to any nation that seceded, so it didn't really matter. Many nations did secede from Russia, including Finland. However, most of those nations were indeed taken over by Bolsheviks, and became puppet states of Russia that were eventually reunified in the Soviet Union. In Finland, just like in all of those countries, there was a civil war between the Whites and the Reds following their secession, but the Whites defeated the Reds, which allowed them to escape enslavement in the Soviet Union.