What is seed metric?

In OSPF , routes are redistributed with default metric that is 20,we call this metric 20 seed metric.

Whenever we redistribute some route information from one routing domain to another, we provide some metric value manually that is what we call "Seed Metric"

We seeds some value manually because of metric compatibility issue in between different routing protocols.

In case of RIP it's hope count, In EIGRP we have complex formula involving bandwidth, delay, reliability and load. etc...