nimitta - Thubten Chodron

The sign or mental image that is the object for cultivating serenity. It is of three types: the preliminary, learning, and counterpart nimittas.

The five faults and eight antidotes
Explanation of Maitreya's teaching on cultivating serenity through overcoming the obstacles.
Meditative stability
Teaching on the conditions and objects of focus for engaging in the far-reaching practice of meditative stability.
Chapter 5: Concentration: Sanskrit and Chinese traditions
Meditative absorptions beyond the ninth stage of sustained attention, and meditative paths to the union of serenity and insight.