The plane of existence is a concept in the Chozo belief system, mentioned once in Metroid Prime. A statue in the Chozo Ice Temple, a place of worship in the Phendrana Drifts depicts a Chozo holding a plate in its hands, representing the plane of existence. This plate can be used as a platform by Samus to ascend the Temple and reach the Wave Beam.
Exactly what the plane of existence refers to is unknown. It is most likely a theological reference to the cosmos as a whole, or a belief in transcendence of the physical realm. Chozo Lore entries occasionally refer to their mastery of time and space.
"A statue depicting a Chozo balancing the plane of existence on his hands.