Displacement
Definition
The straight-line change in position from start to finish — how far you ended up from where you began, and in which direction.
Symbol: · Unit: meter (m)
Technical definition
The vector difference between final and initial position, Δx = x_final − x_initial. Its magnitude is the shortest distance between the endpoints, independent of the path taken.
Example
Walk 3 km east, then 3 km west. Your total distance walked is 6 km, but your displacement is zero — you ended exactly where you started, so the vector sum cancels out.
Displacement is not distance. Distance counts every step of the path (a scalar, always positive); displacement only cares about endpoints (a vector, can be zero or negative). Confusing them breaks every kinematics equation, because those equations are written in terms of displacement — plug in total path length and the math silently gives the wrong answer.