"The endless knot iconography symbolised Samsara i.e., the endless cycle of suffering of birth, death and rebirth within Tibetan Buddhism"
When related to the theory of karma it is the cycle of death and rebirth
According to Monier-Williams, saṃsāra is rooted in the term Saṃsṛ (संसृ), which means "to go round, revolve, pass through a succession of states, to go towards or obtain, moving in a circuit".[20] A conceptual form from this root appears in ancient texts as saṃsaraṇa, which means "going around through a succession of states, birth, rebirth of living beings and the world