Definitions
Use <defs> to define objects (shapes, filters, gradients, etc.).
Objects defined inside <defs> will not be rendered directly. To use them, you need to reference them using their id attribute.
<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
<defs>
<!-- define a circle, id="myCircle"-->
<circle id="myCircle" cx="0" cy="0" r="50" />
<!-- define a gradient, id="myGradient" -->
<linearGradient id="myGradient" gradientTransform="rotate(90)">
<stop offset="20%" stop-color="gold" />
<stop offset="90%" stop-color="red" />
</linearGradient>
</defs>
<!-- use defined items -->
<use x="50" y="50" href="#myCircle" fill="url('#myGradient')" />
</svg> | LIVE PREVIEW