The English word equanimity refers to a state of being calm and balanced, especially in the midst of difficulty. In Buddhism, equanimity is one of the four great virtues (with compassion, loving kindness, and sympathetic joy) that the Buddha taught his disciples to cultivate.
Many years ago, a friend gave me a book on Buddhism; she hoped that reading it would help me chill out. The author encouraged the reader to attain a state of cheerful equanimity. Think Dali Lama. I've been working on it ever since.