Line is the path left by a moving point. For example, a pencil or a brush dipped in paint.
A line can take many forms. It can be horizontal, diagonal or curved. It can also change over its length, starting off curved and ending up horizontal, for example.
Line can be used to show many different qualities, such as:
contours - showing the shape and form of something
feelings or expressions - a short, hard line gives a different feeling to a more flowing one