1. Change in speed: This is the most straightforward way. An object accelerates when its speed increases or decreases. Think of a car speeding up or slowing down.

2. Change in direction: Even if an object maintains a constant speed, it can still accelerate if it changes direction. Imagine a car going around a curve at a steady speed. It's still accelerating because its direction is changing.

In essence, acceleration is any change in an object's velocity, which encompasses both speed and direction.