Length, width, and thickness (or height) are the three axes that extend into three-dimensional space when measuring a three-dimensional object. Distance is the measurement between two distinct points along a line segment.
According to Dictionary.com, length is measured along an object’s longest axis. Width is the longest dimension of an item that is perpendicular to its length along the same geometric plane as its length. Height (or thickness) is the measurement of the axis connecting the highest and lowest points of an object that travels perpendicular to the plane created by its length and width.
The tabletop of a rectangular table, for example, is an immediately identifiable geometric plane. Length is the longest measurement of the tabletop, width is the shortest, and height is the length of any of the table legs (since they would all be the same length).
Also, the dimensions of a book are an example of length, width, and thickness measures. The length is the length of the spine, the width is the distance across the top of the book, and the height is the thickness of the pages.