agonizing decision; painful choice
A decision made after much anguish and internal struggle; often used in formal or serious contexts.
He made an agonizing decision.
The company closed the factory in a painful decision.
苦渋 is a noun meaning 'bitter anguish' or 'agony'; 苦渋の決断 is a fixed phrase using it attributively.
決断 means 'decision' or 'resolution'; 苦渋の決断 specifies a decision made with great difficulty.
Compound of 苦渋 (bitter anguish) + の (attributive particle) + 決断 (decision). The phrase is a set expression describing a decision reached through painful deliberation.