What is the name given to molten rock above ground?

Lava. In the Hawai'ian language, there are two words for lava, depending on what it looks like when it cools.

Pahoehoe is smooth; once it cools, you can easily walk on it. A'a is sharp and spiky; if you walk on it barefoot, you'll cut your feet to ribbons. Walking on a'a lava with boots will cut up the soles of your boots.