Asphalt
Asphalt is a thick, sticky black mix used to pave roads and coat surfaces.
Think of it this way
Honey in a jar is thin and pours when warm, but turns thick and sticky when cold. Asphalt works the same way. It starts as a dark, gooey paste that spreads flat and fills in cracks. When it cools, it hardens into a tough, smooth layer that sticks tight to the ground.
Explaining asphalt by grade level
Asphalt is dark and sticky like tar. When you heat it, it gets soft. Mix it with small rocks and it holds them tight. That is how roads get made.