The Baltic Way, or Baltic Chain, refers to a peaceful protest against communist rule in the Baltic nations.
On August 23, 1989, over a million inhabitants from Latvia, Lithuania, and Estonia held hands across the three states and demanded an end to Soviet occupation and a reinstatement of independence for the Baltic states. The human chain was 600 km, or about 373 miles, long. Another of its nicknames is "the Singing Revolution."
Though the three nations had been under Soviet rule for the past 50 years following World War II, the nations were previously independent. The fiercely independent citizens formed national movements, and the Baltic Chain was itself a joint effort of the Popular Front of Estonia Rahvarinne, the Popular Front of Latvia, and the Lithuanian Reform Movement Sąjūdis.
The protest took place on the 50th anniversary of the Molotov-Ribbentrop Pact, the non-aggression pact between Nazi Germany and Soviet Russia that marked the beginning of Soviet expansion into eastern Europe. During the protest, Baltic people spoke of illegal Soviet occupation and attempted to appeal to others on a moral level as to why the Baltic states should regain independence. Though the USSR responded to the protests with rhetoric, the government did not respond very much, and so the Baltic nations strayed even further from the USSR. The USSR, in its decline, neither brutally cracked down on the rebellion nor responded positively.
The peaceful movement inspired many democratic reforms and movements throughout the rest of the USSR, and the Baltic nations soon afterwards succeeded in a peaceful transition to independence as the Soviet Union collapsed for good in 1991.
Sources: BBC.co.uk, Baltic Way.net, Wikipedia