Short answers, pulled from the story.
The First Jassy-Kishinev offensive was a series of Soviet military engagements against Axis forces in Romania, named after the cities of Iași and Chișinău. According to David Glantz, it ran from the 8th of April to the 6th of June 1944; Richard C. Hall dates its start to the 5th of April 1944.
The Red Army's 2nd and 3rd Ukrainian Fronts conducted the operation. Key commanders included Marshal Ivan Konev of the 2nd Ukrainian Front, Semyon Bogdanov's 2nd Tank Army, Konstantin Koroteev's 52nd Army, and elements of Andrei Gravchenko's 6th Tank Army.
David Glantz attributes the failure primarily to poor combat performance by Soviet troops and the effectiveness of German defensive preparations around Târgu Frumos. The German Military History Research Office also credits bad weather conditions, which Axis forces used to achieve a defensive success.
According to Glantz, Stalin ordered the offensive to break German and Romanian defenses in northern Romania, capture Iași and Chișinău, and then project Soviet forces deep into Romanian territory, potentially as far as Ploiești and Bucharest, extending Soviet influence across the Balkans.
Glantz argues that Soviet and Russian military historians deliberately erased the operation from the historical record during the nearly sixty years following the Second World War, placing it among the 'forgotten battles' of the Soviet-German War because it ended in failure.
Historians dispute its very nature. Glantz treats it as a genuine coordinated offensive that was launched and repulsed. The German Military History Research Office holds that the threatened Soviet push in northern Moldavia 'failed to materialize' in the first part of April 1944, and that Stavka ordered a halt to offensive actions in the sector on the 6th of May.