Yoga is one of the six classical schools (Darshanas) of Indian philosophy. There are many different forms of yoga, often each with its own philosophy and practice. Until recently, in Europe and North America, the term yoga often referred only to physical exercises - the asanas or yogasanas. Some meditative forms of yoga focus on mental concentration, while others emphasize physical exercises and positions as well as breathing exercises (Pranayama), and some traditions stress asceticism. The philosophical foundations of yoga were primarily summarized by Patanjali in the Yoga Sutras, and the Bhagavad Gita and the Upanishads also provide insights into yoga. Today, yoga practices generally pursue a holistic approach aimed at harmonizing body, mind, and soul. Especially in Western countries, yoga is often taught in structured classes.