Ukraine wants a 'NATO-esque' bloc which can be called upon to immediately defend borders with Russia, which was proposed by a working group established by President Volodymyr Zelensky. Crucially it would include the United States and other NATO allies providing Ukraine with "security guarantees".  Kiev officials stressed in unveiling the plan Tuesday that it's not meant as a replacement for NATO, but as a legally binding alliance to be in place while Ukraine eventually pursues full NATO membership, as Newsweek describes of the proposal: 

The Kyiv Security Compact (KSC)—proposed by Andriy Yermak, the head of Zelensky's office, and former NATO Secretary-General Anders Fogh Rasmussen—would also establish a "multi-decade" plan of investment, military training, and intelligence sharing to bolster Ukraine's defensive capabilities as the country pursues full NATO membership.

The Kremlin's reaction has been swift and fierce, with Deputy Chairman of the Security Council of Russia Dmitry Medvedev warning that it is "really a prologue to the Third World War" if it gets enacted. He described that nuclear holocaust would be the end result.