Depending on the intensity and the depth, three different kinds of Samadhi have been named: Savikalpa Samadhi (also spelled Sabikalpa), Nirvikalpa Samadhi (also spelled Nirbikalpa) and Sahaja Samadhi. But since Samadhi means being in the state of undifferentiated Beingness, there aren't really different kinds of Samadhi at all. The difference is only seen from our point of view.
Savikalpa Samadhi refers to the beginning state of Samadhi while Nirvikalpa Samadhi is the end result. During the beginning states, we might enter a form of Samadhi where we get the taste of Bliss and Beingness but we still hold tight to our erroneous identification with the body as well as to our numerous worldly attractions. Entering Samadhi in the beginning takes effort and holding on to Samadhi takes even more effort. Beginning stages of Samadhi are only temporary.
Upon entering Nirvikalpa Samadhi the differences we saw before have faded and only one and the same Substance is seen with which we then gladly identify. In this condition nothing but pure Awareness remains and nothing is missing to take away from Wholeness and Perfection. Samadhi is the only stable Reality, everything else is changing and does not bring everlasting peace or happiness.Staying in Nirvikalpa Samadhi is effortless but even from this condition one must eventually return to ego-consciousness - however, it is entirely possible to stay in Nirvikalpa Samadhi and still be fully functional in this world. This condition is known as Sahaja Nirvikalpa Samadhi.