The term 'Volcano Apex' refers to the highest point of a volcano, which is typically a CONE-shaped structure. The crossword solution for this term is 'CONE, ' which is a four-letter word. A volcano apex is formed when molten rock and ash are ejected from the volcano's vent and accumulate around the opening. This accumulation of material builds up over time, forming a CONE-shaped structure at the top of the volcano.