Impact means the force or effect when one thing hits another, or the powerful influence something has. When a meteorite strikes Earth, the impact creates a crater. When you drop a water balloon from a roof, you hear the impact as it splats on the ground.

The word also describes how much something matters or changes things. A great teacher can have a tremendous impact on students' lives, shaping how they think and what they pursue. A new invention might have an enormous impact on how people live. Scientists study the impact of ocean currents on marine life.

You'll often hear people say something made an impact or had an impact. A moving speech might make an impact on listeners, changing how they think about an issue. A charity might measure its impact by counting how many families it helped.

Notice that impact suggests something significant and noticeable, not minor or trivial. A small change might affect something, but we usually save the word impact for changes or collisions that really matter, leaving a mark or creating lasting effects.