Prompt sensitive tasks are natural language processing tasks for which a language model's predictions or performance vary significantly when presented with minor rephrasings, perturbations, or stylistic variations in the input instructions. On such tasks, the model exhibits high output disagreement and uncertainty across semantically equivalent prompts, reflecting fragile or ambiguous comprehension rather than complete mastery or definitive failure. In machine learning paradigms such as active instruction tuning, identifying and prioritizing prompt sensitive tasks allows practitioners to select highly informative training data, helping the model resolve instructional ambiguities, achieve greater robustness to prompt variation, and improve generalizability across unseen tasks with higher data efficiency.