(Sanskrit संसार; Tibetan khorwa or khor-ba) Literally, "to flow on; circling." Samsara refers to the state of consciousness that is conditioned by subjective psychological factors, called sins, samskaras, egos, defects, aggregates. Samsara is cyclic, conditioned existence whose defining characteristic is suffering. It is contrasted with nirvana. Although the term is commonly used to refer to the realms of nature (such as the physical world or the hell realms), beings only exist in such realms because their minds are conditioned.
"Samsara is your mind’s deluded form." —Padmasambhava, Descending with the View from Above
“Cyclic existence [samsara], which is full of attachments, aversions, etc., is like a dream. It appears to be real as long as one is ignorant, but becomes unreal when one is awake.” —Shankaracharya, Atma Bodha 6
"All beings have lived and died and been reborn countless times. Over and over again they have experienced the indescribable Clear Light. But because they are obscured by the darkness of ignorance, they wander endlessly in a limitless samsara." —Padmasambhava
"Samsara - our conditioned existence in the perpetual cycle of habitual tendencies — and nirvana, genuine freedom from such an existence, are nothing but different manifestations of a basic continuum. So this continuity of consciousness is always present. This is the meaning of tantra. According to Buddhist practice, there are three stages or steps. The initial stage is to reduce attachment towards life. The second stage is the elimination of desire and attachment to this samsara. Then in the third stage, self-cherishing is eliminated." —The 14th Dalai Lama