LIDAR is a technology where a scanner emits pulses of light energy (using a laser) at buildings and other objects in an area, and measures how long it takes for the pulse to return. The laser pulse travels at the speed of light. Accordingly, the distance it travels can be calculated by multiplying the amount of time it takes for the pulse to arrive back at the scanner, with the speed of light, and dividing that figure by two (since the pulse makes a round trip).
Helpful LIDAR Articles:
How to Use LIDAR in Aurora
Where is LIDAR available in Aurora?
How to Move Trees in 3D to Fit LIDAR