A vector is a quantity that has both size and direction. Think of it like an arrow: the length of the arrow shows how much, and the way it points shows which way. If you're walking to school, your velocity is a vector because it describes both how fast you're moving (say, 3 miles per hour) and which direction you're heading (north). Just saying “3 miles per hour” only gives speed, but adding direction makes it velocity, a true vector.

Vectors are essential in physics and mathematics. When engineers design a bridge, they use vectors to understand all the different forces pushing and pulling on it. When video game programmers make a character move across the screen, they use vectors to control both speed and direction. Even weather forecasters use vectors to show wind: the arrows on weather maps point in the direction the wind is blowing, and their length shows how strong it is.

You can add vectors together, subtract them, or break them into parts, which makes them powerful tools for solving problems about motion, forces, and change.

In biology, a vector means something completely different: an organism that carries and transmits disease, like a mosquito spreading malaria.