Marine describes anything related to the ocean or sea. Marine life includes all the creatures living in salt water: whales, dolphins, sea turtles, jellyfish, octopuses, and the countless fish species swimming through coral reefs and deep ocean trenches. Marine biology is the science of studying these ocean creatures and their habitats.

When scientists talk about the marine environment, they mean the oceans and everything in them. Marine ecosystems include not just the open ocean but also tide pools, coral reefs, and coastal areas where salt water and land meet.

Marine can also refer to sailors and naval forces. Marines are members of a branch of the military trained to fight on land and sea, originally soldiers who served aboard naval ships. They're known for their toughness and distinctive uniforms.

You might encounter marine in everyday phrases too. Marine-grade materials are built to withstand salt water and harsh ocean conditions, like the special rope and hardware used on sailboats. A marine layer is the thick fog that rolls in from the ocean on coastal mornings, formed when cool marine air meets warmer land.