These are actually two slightly different options. Mouse sensitivity is how far the cursor or camera moves based on how far the mouse moves. More sensitivity means that the camera moves more if you move the mouse the same distance.

Mouse acceleration tracks how fast the mouse moves over that distance and extends the amount the camera or cursor moves if it moves faster or decreases it if it moves slower. In some cases this can feel more natural, but in others it can make it harder to be both fast and precise in your movements, since moving faster can make you overshoot compared to making the same movement more slowly.