"Differential flatness" is synonymous to "flatness". The concept is a bit comparable to inverse kinematics. With inverse kinematics you compute, e.g. the joint

"Differential flatness" is synonymous to "flatness". The concept is a bit comparable to inverse kinematics. With inverse kinematics you compute, e.g. the joint angles of a robot arm given its endeffector pose. While with differential flatness you use the pose trajectory and its derivatives (i.e. how the pose changes over time) to calculate the state trajectory (joint angles, speeds and accelerations for the robot arm example).