Bird watching: what does pelagic mean?

Self-tutoring about birds: the tutor mentions the term “pelagic.”

What does “pelagic” mean? It refers to the surface of the ocean, but out of reach of shore. Some birds are pelagic, meaning you can’t see them from land. The black-footed albatross is an example: the guide says you must go “at least 15 km” into open ocean to see one (along BC’s west coast).

Source:

Hoar, Tyler L. et al. Birds of Canada. Edmonton: Lone Pine, 2010.