Flight dynamics is the study of orientation of aircraft and space vehicles and how to control the critical flight parameters, typically named pitch, roll and yaw.
Pitch is rotation around the lateral or transverse axis of rotation. This axis is parallel to the wings, thus the nose and tail both pitch up or down. An aircraft pitches up to climb and pitches down to dive.
Roll is rotation around the longitudinal axis—an axis drawn through the body of the vehicle from tail to nose. This is also known as bank.
Yaw is rotation about the normal axis—an axis perpendicular to the pitch and roll axes. If an airplane model placed on a flat surface is spun or pivoted around the center of mass it would be described as yawing.
Aerospace engineers develop control laws and control systems to allow pilots to control their aircraft in the three dimensions described above.