Samsara - the endless cycle of death and rebirth.

10 realms or existence - hell, hungry spirits, animals, fighting beings (ashuras), humans, celestial beings (these are the 6 lower realms into which you can transmigrate/reincarnate)

pratyeka buddhas, shravakas, bodhisattvas, buddhas/tathagata (these are the 4 higher realms, no longer subject to reincarnation)

sentient beings - any being that has life.