Rear is used to refer to the part of something such as a building or vehicle that is towards the back or nearest to the back.

The rear of something such as a building or vehicle is the back part of it.

If you are at the rear of a moving line of people, you are the last person in it.

Your rear is the part of your body that you sit on.

If a person or vehicle is bringing up the rear, they are the last person or vehicle in a moving line of them.

If you rear children, you take care of them until they are old enough to take care of themselves.

If you rear a young animal, you keep and take care of it until it is old enough to be used for work or food, or until it can look after itself.

When a horse rears, it moves the front part of its body upwards, so that its front legs are high in the air and it is standing on its back legs.