Drag force

Drag is the force a fluid pushes back with. AP Physics C: Mechanics files it under resistive forces and defines one as a velocity dependent force in the opposite direction of an object's velocity, giving $F_r = -kv$ as its example.

That linear model is the one the course actually solves. Applying Newton's second law to an object on which a resistive force is exerted produces a differential equation for velocity, which the CED handles by separation of variables, integrating over the proper limits. It then states that the position, velocity and acceleration as functions of time under a resistive force of the form $F_r = -kv$ are exponential, with asymptotes determined by the initial conditions and the forces exerted on the object.

The quadratic model, drag proportional to $v^2$, is the better description of fast motion through air, but it is not the form the CED develops, and no AP equation sheet prints a drag equation at all.

Terminal condition: the CED defines terminal velocity as the maximum speed achieved by an object moving under a constant force and a resistive force exerted in opposite directions, reached when the net force on the object is zero. With gravity and $F_r = -kv$ that gives $v = mg/k$.

The algebra based courses leave drag out by default. The AP Physics 1 CED's list of modeling assumptions says that unless otherwise stated, students may assume air resistance is negligible.