A shark is a type of fish that has lived in Earth's oceans for over 400 million years, making sharks older than trees and dinosaurs. Unlike most fish, sharks have skeletons made of cartilage (the same flexible material in your nose and ears) instead of bone, which makes them lighter and more agile in water.

Sharks come in astonishing variety. The whale shark grows longer than a school bus and eats only tiny plankton. The dwarf lanternshark fits in your hand. The great white shark, made famous by the movie Jaws, is a powerful predator with rows of replaceable teeth. Most sharks never threaten humans: you're far more likely to be struck by lightning than attacked by a shark.

People also use shark to describe someone who's ruthlessly competitive or who takes advantage of others. A pool shark is highly skilled at billiards. A loan shark lends money at unfairly high interest rates. In business, shark can describe someone who's aggressive and calculating, always looking for their next opportunity. When lawyers compete intensely for clients, people might call them sharks.

The word can also be a verb: to shark means to get something through trickery or aggressive pursuit, though this usage is less common.