Original: A fumarole (Latin fumus, smoke) is an opening in Earth's (or any other astronomical body's) crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide.
Simplified: A fumarole (Latin fumus, smoke) is an opening in the crust of the Earth, often in the neighborhood of volcanoes, where steam and gases come out, for instance carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide.