A: The word “terminal” means “extreme” - so terminal velocity means an extreme or maximum velocity achieved as an object falls through the air due to gravitational force.
Now one may ask: how is this maximum velocity achieved? To understand this, we have to acknowledge the two forces acting on an object falling down: weight acting downwards, and air resistance acting upwards. Initially when the object starts falling, the weight is greater than air resistance, and so the object accelerates (i.e. its velocity increases). But as velocity increases, the air resistance also increases - until there comes a time when air resistance equals weight. That’s a critical point when the resultant force becomes zero, thus achieving a state of constant velocity.
This constant velocity is what we call terminal velocity - and it is the maximum value that the object can attain!