दुःखेष्वनुद्विग्नमनाः सुखेषु विगतस्पृहः। वीतरागभयक्रोधः स्थितधीर्मुनिरुच्यते ॥

duḥkheṣhv-anudvigna-manāḥ sukheṣhu vigata-spṛihaḥ vīta-rāga-bhaya-krodhaḥ sthita-dhīr munir uchyate

He whose mind is free from anxiety amid pains, indifferent amid pleasures, loosed from passion, fear and anger, is called a sage of stable mind.

In plain words: A wise person with a steady mind is not shaken when bad things happen and does not chase after pleasures. They are free from strong craving, fear and anger.