Samsara is the Sanskrit for “cyclic life” or korwa (Tibetan)
The definition in Tibetan is:
sakche nyerlen gyi pungpoy gyun yagne yangdu lenpa ni korwa yin
which is translated:
Samsara is the condition of having to take on, over and over again, a stream of impure parts (heaps or aggregates) which were forced on you.
The Tibetan word pungpoy refers to something like a heap or pile. The Sanskrit is skandha which is usually translated as aggregates.
The Tibetan word nyerlen implies that you are forced (by karma in this case) to take on the impure parts.
The idea of samsara and being forced to be reborn is central to the Buddha’s teachings and in contrast to some spiritual schools of thought that believe we choose to come into this world in order to learn lessons that we have likewise chosen to learn. This is an interesting samsaric idea, but closer examination of the mind reveals how little choice we have in our unenlightened state.
Enlightenment marks the end of samsara as evidenced in the Buddha’s words:
Through countless births in the cycle of existence I have run, not finding although seeking the builder of this house; and again and again I have faced the suffering of new birth.
Oh housebuilder! Now you are seen.
You shall not build a house again for me.
All your beams are broken, the ridgepole is shattered.
The mind has become freed from conditioning; the end of craving has been reached.
—Dhammapada XI. 8&9 (153&154)