Preference allows you to set an "administrative distance" for the route that is used to to convey the "believability/trustworthyness" of a route.
The various dynamic routing protocols each have unique administrative distances.
Normally static routes would be interpreted as more believable because of their lower default administrative distance.
However, you could create a "floating static route" by specifying an administrative distance greater than the the AD of your dynamic routing protocol.
When the dynamic route is lost, the floating static route will be placed into the routing table. This can be utilized for many purposes.
e.g.: Bringing up a backup link.
I'll assume metric was the term more familiar to you. The other poster has graciously provided a link if you need to pursue your comparison further.
