LiDAR (Light Imaging Detection and Ranging) is an optical remote sensing technology which measures the properties of the light bouncing off the earths surface to determine distance and other information. In simple terms, the laser bounces off the earth's surface which produces a data set to extract products such as an elevation model of the earth's surface.
An orthophoto is an aerial photograph which has been geometrically corrected. The scale of the orthophoto is uniform and can be used to measure true distances. In simple terms, it is an aerial photo which has control points (features in the photo such as a road intersection) which are used to move the photo to that coordinate position of the feature.