The 4 Jhanas

The Jhanas and the practise of Jhana Access Meditation techniques is in the present day rather largely misunderstood and has grown to be less promoted as a path of practise in many Buddhist lineages. However, the Suttas display evidence of the Lord Buddha repeatedly mentioning and recommending the use of Jhana Absorbtion meditation methods as an access route to Nibbana. To Explain the Jhanas in their basic conceptual meaning, I find there is till now no better teaching to recommend for those seeking an understanding of what Jhana Meditation is, and what it entails in order to be able to practise this form of mental absorbtion method, than that of Henepola Gunaratana (Lovingly known by his devotees as "Bhante G"), of the Bhavana Society
You can read his concise and easy to grasp explanation here; The Jhanas - Henepola Gunaratana