Jhāna generally refers to the 8 stages of tranquility (samatha) meditation taught by Gautama Buddha and mentioned in the Pali Canon.
Jhāna (Pali, Dhyāna in Sanskrit) refers to the 8 stages of meditation that were taught by Gautama Buddha. The word Jhāna stems from jhayati which means 'think' or 'meditate'. These 8 states of altered consciousness, which can arise can during periods of strong concentration, are also simply called 'the Jhānas'.
The Jhānas are mentioned in the Pali Canon, but not all Buddhist traditions regard them as important. In Theravada Buddhism the Jhānas are considered an important means to obtain wisdom and ultimately to reach Nirvana. Some other traditions however consider the Jhānas as dangerous because they are not an insight practice and one can become attached to them.