If you have ever looked in between bricks on a brick house, you should see a thin layer of whitish-beige color. When you touch this, it may feel like cement, but it is actually a mixture of cement, sand and water. This is called mortar. Mortar like cement dries fairly quickly and it also dries hard. That is why it is used with bricks. Mortar will keep the bricks in place.
Over many years, the mortar may crack from weather. Mortar is also used between stones and other types of material. When a truck is transporting mortar or cement from one location to another, it must constantly turn. Otherwise, it will dry before the mortar gets to the location. You may be able to identify these trucks because they are usually orange and white striped trucks that spin the cement.