(Sanskrit समाधि) Literally means “union” or “combination,” although in context it can have a dizzying number of meanings (see below). Its Tibetan equivalent means “adhering to that which is profound and definitive,” or ting nge dzin, meaning “To hold unwaveringly, so there is no movement.” Related terms include satori, ecstasy, manteia, etc. Samadhi is a state of consciousness. There are many levels of Samadhi.
In general, the word refers to the ultimate stage of yoga, in which the consciousness, freed of the conditioning of the body and mind, experiences its true nature: happiness, insight, joy, freedom, etc. This experience is reached and perfected only through meditation.
See: What is Samadhi?