Drawing on the Canvas - HTML5 Canvas - page 67

Using Paths to Create Lines
Paths are a method we can use to draw any shape on the canvas. A path is simply a list
of points, and lines to be drawn between those points. A Canvas context can have only a
single “current” path, which is not stored as part of the current drawing state when the con-
text.save() method is called.
Context for paths is a critical concept to understand, because it will enable you to transform
only the current path on the canvas.