Short answers, pulled from the story.
Retrograde motion is orbital or rotational movement against the rotation of its primary body. This classification depends on inclination angles measured from 90 to 180 degrees relative to an inertial frame of reference.
All eight planets orbit counterclockwise when viewed from above the Sun's north pole and follow standard prograde paths. Six planets also rotate about their axis in this same direction as they orbit.
Venus possesses an axial tilt of 177 degrees and rotates almost exactly opposite to its orbital path. Gravitational tidal dissipation near the Sun interacts with thick atmospheric tides to create a retrograde torque that evolved it from a primordial fast prograde rotation.
Astronomers determine this direction using an inertial frame of reference like distant fixed stars. An angle between 90 and 180 degrees indicates a retrograde orbit while an angle between 0 and 90 degrees signals prograde motion.
Neptune's moon Triton stands as the largest satellite in the Solar System yet follows a retrograde orbit. Tidal deceleration affects all retrograde satellites but remains negligible for most except Triton.