As one progresses in the spiritual quest, one gets introduced to various ideas and concepts. In general the drive for spirituality arises from a desire to get into a certain state where the experiences are the way that one wants them to be. Typically the desire is a world without suffering, and one that is full of joy. In religious terms one may call that Heaven. A holiday resort promises us to give such an experience though momentarily. We escape from the irritants of life and taste a bit of tranquility. This tranquility, or Euphoria or other such enjoyable moments makes us crave for more of it. But the experiences that we get are always a combination of things. Never are they the way we want them to be.
Scriptures tell us that Samadhi is such a state where one lives in total joy devoid of suffering. A more common easily reachable state that we all experience is a deep sound sleep devoid of dreams. We always enjoy deep sleep, even though we would not be aware of it while we are sleeping. But after we come out of that deep sleep, the mind feels rested well and refreshed. The purposefulness of such a deep sleep is not the sleep itself, but the fact that it appears to help us in our waking state. We relish the fact that we had a nice sleep, but we can only think about it while we are awake.
The wakeful state is the only state that we have access to. All other states do not exist in the Now. Samadhi is also similar to deep sleep, a state of silence. There are different kinds of samadhi. Nirvikalpa, Savikalpa, Sahaja etc.. and this state of silence is graded depending on if one is aware of the world while in this state, or to what extent one is aware etc. All experiences that take one away from the waking state, cannot be experienced. Its a contradiction. An experience that can not be experienced! what can that be? It cannot be anything.
A craving of the mind for some deep mystical experiences, has resulted in a notion of some physical experience being associated with Samadhi.
Samadhi is a concept or an idea, that promises a state of joy. Understanding the truth about who you are and what the world is, is Knowledge. This Knowledge removes all suffering and results in Joy. Staying in this Knowledge as one goes about in life is Samadhi.