Short answers, pulled from the story.
Demokratizatsiya was a slogan introduced by CPSU General Secretary Mikhail Gorbachev in January 1987. It called for multi-candidate, though not multi-party, elections for local Communist Party officials and soviets, while the CPSU retained sole control of the ballot box. The policy was part of a broader reform package that also included glasnost and perestroika.
Gorbachev introduced demokratizatsiya in January 1987. He had outlined earlier reform goals at the Twenty-Seventh Party Congress in February 1986, but concluded those goals required a new strategy of appealing directly to the Soviet people over the heads of party officials.
Demokratizatsiya allowed multiple candidates to compete for the same office but kept all candidates within the single-party framework of the CPSU. The Communist Party retained sole custody of the ballot box. Despite this limitation, elements of a genuine multiparty system began forming as a consequence of the reforms.
The March 1989 election was the first time Soviet voters chose the membership of a national legislative body. Voters across the country crossed off the names of unopposed Communist candidates, including many prominent party officials. The resulting Congress still contained 87 percent CPSU members, but genuine reformists won around 300 seats.
Article 6 enshrined the CPSU's supremacy over all institutions in Soviet society. As opposition pressure from the Inter-Regional Group in the Congress of People's Deputies mounted, Gorbachev obtained the repeal of Article 6 at the February 1990 Central Committee plenum. Its removal stripped the legal foundation from the one-party state.
By the time of the Twenty-Eighth Party Congress in July 1990, the republics of the Soviet Union were pulling harder than ever toward independence. CPSU branches in the fifteen Soviet republics split into pro-sovereignty and pro-union factions. The party was separated from government, stripped of its leading societal role, and the union itself began to dismantle.