A trajectory is the path that something follows as it moves through space. When you throw a ball, it follows a curved trajectory as gravity pulls it back down to Earth. A basketball arcing toward the hoop, a soccer ball curving past a goalie, or a paper airplane gliding across a classroom: each traces its own trajectory through the air.

The word comes from physics and mathematics, where scientists study how objects move. A rocket launching into space follows a carefully calculated trajectory. Meteorologists track the trajectory of hurricanes to predict where they'll make landfall. Understanding trajectories helps engineers design everything from water fountains to satellites.

People also use trajectory to describe how situations or lives develop over time. A student on an upward trajectory is improving steadily in their studies. A business on a downward trajectory is losing customers and money. When someone talks about your “life trajectory,” they mean the general direction your choices and circumstances are taking you. Just like you can change a ball's trajectory by throwing it differently, people can change their life trajectories through their decisions, effort, and persistence.