In physics, "jerk" refers to the rate of change of acceleration with respect to time. It represents the third derivative of an object's displacement with respect to time. In other words, jerk is the measure of how quickly the acceleration of an object is changing.

Mathematically, jerk (denoted by "j") is expressed as:

j = d³x/dt³

where:

• j is the jerk of the object,
• dx/dt is the first derivative of displacement (velocity) with respect to time (rate of change of position),
• d²x/dt² is the second derivative of displacement (acceleration) with respect to time (rate of change of velocity), and
• d³x/dt³ is the third derivative of displacement (jerk) with respect to time (rate of change of acceleration).