The Abyss of Life and Death is a spiritual plane of existence where wavering souls are transported.
Shortly after Clark Kent stabbed himself with a dagger with blue kryptonite, his soul arrived at the Abyss and was faltering on the edge of life and death itself. Because Clark didn't cross over right away, Jor-El was able to talk to him. After enduring Jor-El's condescending remarks, Clark saw Lex Luthor. Immediately afterwards, Lois Lane removed the dagger from Clark's body, causing the spiritual backlash to return Clark's soul to his body while Lex's soul went into his composite clone.