def. continuous mark made on some surface by a moving point.
The most obvious: A line that starts at point "A" and ends at point "B"
These two pictures are clear representations of line because they have a starting point and an ending point. (Think math or graphs)
Getting Creative: When using line to compose a photo or other forms of art. Line is used to focus the viewers attention on the main focus and usually directs where the viewer should look. This can be seen in the photo directly below (taken by me).
In this photo, I used the repetitive lines of the fence to direct the attention of the viewer to my friend, the focal point. The lines emphasize my friend but also evoke a dark mood. The tight lines draw closeness and are reminicent of a jail cell.