A whale is any of several massive ocean mammals that breathe air, nurse their young with milk, and spend their entire lives in the sea. The blue whale is the largest animal ever known to exist on Earth, heavier than even the biggest dinosaurs. Despite their size, whales are graceful swimmers, using their powerful tails to glide through the ocean.

Whales include dozens of species, from enormous blue whales and humpbacks to smaller (but still large!) orcas and belugas. They're intelligent creatures that communicate with complex songs and clicks. Some whales, like humpbacks, migrate thousands of miles between feeding and breeding grounds. Others, like sperm whales, dive thousands of feet deep, hunting for giant squid in the dark ocean depths.

People sometimes use whale as a verb meaning to hunt whales, an industry that nearly drove many species to extinction before international protection efforts began. The phrase a whale of a means something exceptionally large or impressive, as in “We had a whale of a good time at the amusement park.”

Whales aren't fish, even though they live underwater.