Nuclear holocaust is another name for a nuclear war or the state of a planet thereafter. It often resulted in nuclear winter.
The Talosians were once a technologically-advanced culture but a nuclear holocaust left Talos IV virtually uninhabitable. (TOS: "The Cage")
Kevin and Rishon Uxbridge were the only survivors of a nuclear holocaust on Delta Rana IV. (TNG: "The Survivors")
Humanity experienced a nuclear holocaust following the Third World War between circa 2026 and 2053. Six hundred million (other sources say 37 million) were killed and major cities were destroyed. This led to the post-atomic horror. (TOS: "Bread and Circuses"; TNG: "Encounter at Farpoint"; Star Trek: First Contact; production art seen in ENT: "In a Mirror, Darkly, Part II")