How it's produced
All aircraft propulsion works by accelerating a mass of air (or combustion products) rearward. By Newton's third law, the reaction force pushes the aircraft forward — that reaction force is thrust.
Different propulsion types move different masses of air at different velocities. Propellers move a large mass of air at relatively low velocity. Jet engines move a smaller mass at very high velocity. Rockets carry their own oxidizer and don't depend on atmospheric air at all.
Quick reference
| Direction | Along the aircraft's thrust axis — roughly forward |
| Opposing force | Drag |
| Measured in | Pounds-force (lbf) or Newtons (N) |
| Sources | Piston engine + propeller, turboprop, turbofan, turbojet, rocket |
| Excess thrust enables | Acceleration, climb, or both |
Thrust and drag operate on one axis; lift and weight on the other. This orthogonal pairing is useful mental scaffolding: the thrust/drag balance governs speed and climb; the lift/weight balance governs altitude. Changing one pair affects the other — more throttle increases speed, which affects how much lift the wings generate.