1. “A line is a dot that went for a walk.”
Elements of Art
Line
The extension of a point, elongated marks, the connection between two points, the effect of the edge of an object.
“A line is a dot that went for a walk.”

2. The line which defines a form or an edge- an outline.
Contour Line

3. Observationally drawing the lines of an object without looking at the paper
Blind Contour

4. Horizontal and vertical lines that imply form on the object.
Cross Contour

5. Gestural Line
A quick, loose expressive line used to warm up and capture the state of the object or position.

6. Thickness, movement, direction, style, open, closed, implied, etc.
Line Variety