Jhāna is the Pali word for meditation and can be translated as 'meditative absorption'. It is a particular form of meditative stabilization, where the quality of concentration deepens to the point of allowing for a sense of peace, joy, or other naturally arising states to manifest. The quality of 'jhānic' experience involves having a clarity and vividness of perception, where phenomena can be seen in vivid detail, without any sense of effort or strain. By stabilizing and deepening into meditative practice, the vipassana or insight practices can be undertaken more effectively.
See also: insight meditation, dependent origination, samadhi practice, metta practice