Understanding the Concept:
Terminal velocity occurs when net force on the body becomes zero due to balance between downward gravitational force and upward drag force.
Step 1: Forces acting on body.
\[
\text{Weight} = mg \quad (\text{downward})
\]
\[
\text{Drag + buoyant force} \quad (\text{upward})
\]
Step 2: At terminal velocity.
\[
\text{Net force} = 0
\Rightarrow F_{\text{net}} = ma = 0
\]
Step 3: Interpretation.
If net force is zero, acceleration must be zero, and velocity remains constant.
Step 4: Final Answer.
\[
\boxed{0}
\]