The polyline element is a basic shape that creates straight lines connecting several points. Usually a polyline is used to create open shapes as the last point doesn't have to be connected to the first point. For closed shapes see the <polygon> element.
<svg xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink">
<polyline fill="none" stroke="black"
points="100 40,60 70,80 100"/>
</svg>Note: The fill attribute! If you do not specify fill=none then the polyline it will fill the space. Have a look. I encourage you to experiment with the polyline.
<svg xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink">
<polyline stroke="black"
points="100 40,60 70,80 100"/>
</svg>