A 5-degree-of-freedom flight sim shooter made by 3-D Realms from circa 1995. The goal is basically to destroy ground targets while avoiding ground-based resistance and taking down enemy fighters. The playing field is a polygon rendered 3-D landscape complete with trees. In addition to eliminated ground and air targets, the game keeps a "organic elements destroyed" score of how many trees you blow up.
The game engine used in Terminal Velocity was bought by Microsoft and used in their 1996 game Fury 3.