Russia's tricolor started life as a merchant ensign. Peter the Great, remaking the Russian navy along Western European lines, took his colors from the Dutch flag and put white, blue, and red on Russian trading ships.
From merchant ensign to state flag
The combination appears in the late 17th century, during the reign of Tsar Alexis I by some accounts and under Peter by others. What is settled is that it was first flown officially in 1696 as a commercial flag, something to identify Russian vessels in foreign ports rather than to represent the state.
The Soviet government replaced it. From 1923 to 1991 the red banner with the hammer, sickle, and star flew in its place. The tricolor was reinstated on August 22, 1991, after the dissolution of the Soviet Union, and that date is now National Flag Day.
What the colors are supposed to mean
None of the color meanings is official. The common reading gives white to nobility and frankness, blue to faithfulness and honesty, and red to courage and love. Other interpretations treat the three stripes as the historical territories of the Russian empire, or map them onto the imperial motto "Orthodoxy, Autocracy, and Nationality."
Protocol
The flag flies at state buildings, on military occasions, and at international institutions, and the rules are specific: it goes above subordinate flags, and it is not to be worn as clothing or used in advertising. It is prominent on Defender of the Fatherland Day and Victory Day. The navy has its own ensign.
Serbia, Slovakia, and the Dutch
Serbia and Slovakia fly horizontal tricolors in the same three colors, which is usually attributed to shared Slavic history. The Dutch link runs in the other direction: Peter admired Dutch naval power, and the colors came back to Russia along with the shipbuilding.
Related terminology
Vexillology supplies the vocabulary, including "field" for the background and "ensign" for a flag flown at sea. Historically the flag is tied to Peter and the Romanov dynasty. In official Russian usage it is the "Gosudarstvenny Flag," the State Flag.