What is start angle and end angle of arc in html5 canvas?

This method takes Six parameters:

• x and y are the coordinates of the circle's center.
• Radius is self explanatory.
• The startAngle and endAngle parameters define the start and end points of the arc in radians. The starting and closing angle are measured from the x axis.
• The anticlockwise parameter is a boolean value which when true draws the arc anticlockwise, otherwise in a clockwise direction.

For better understanding of startAngle and endAngle

http://www.html5canvastutorials.com/tutorials/html5-canvas-arcs/

They are radians, not degrees.

Some good examples