1. Relating to organisms living in open oceans or seas rather than in waters near land or inland waters: Some kinds of birds are known to be pelagic, but also some fish are pelagic-neritic and grow to about 8.0 cm in length.
2. Concerning organisms that live or grow at or near the surface of the ocean, far from land: In Ruth's biology book, she read about pelagial areas in the seas and what organisms dwelled there.
3. Pertaining to the sea; marine: It is possible to find pelagian shells when on vacation near the ocean.

The pelagic zone of the ocean begins at the low tide mark and includes the entire oceanic water column. The pelagic ecosystem is largely dependent on the phytoplankton inhabiting the upper sunlit regions, where most ocean organisms live.

Biodiversity decreases sharply in the unlit zones where water pressure is high, temperatures are cold, and food sources scarce. Pelagic waters are divided, in descending order, into the epipelagic, mesopelagic, bathypelagic, abyssopelagic, and hadopelagic zones.