According to Apte's Sanskrit-English Dictionary the word yoga has more than 40 distinct meanings, most of them unrelated to religion. The closest English equivalent to the word is yoke. In Brahmanism the word meant, as it came to mean in later Hinduism, spiritual practice or discipline, although it is hardly ever used in this sense in the Tipiñaka. The Buddha occasionally used the word yoga in a positive sense. One of the terms for nirvana is `Safety from the Yoke'(yogakhema, S.I,123), `yoked to Dhamma' (yogadhamma) means having a strong commitment to spiritual practice (A.III,335), and an arahat is sometimes referred to as a `yoke conquerer' (yogàtiga, It.61). However, in the Tipiñaka yoga more usually associated with the negative. The mental defilements (àsava) are sometimes also called yokes (A.II,10),  

For most people today however, the word yoga is associated with the ancient system of physical and mental exercises commonly called hatha yoga. The basic text of hatha yoga  is the 383-verse Hathayogapradipikà in four chapters, each dealing with postures (àsana), breathing (pràõayàma), gestures (mudrà) and concentration (samàdhi). This work is difficult to date but was probably composed between the 14th and 15th centuries CE. Although a Hindu discipline, anyone doing Buddhist meditation will find that hatha yoga benefits their practice. It enhances good health, it can be a type of mindfulness of the body and it can invigorate the body after extended periods of meditation.