Secondary hemostasis is the series of interrelated chemical processes which lead to the formation of durable fibrin strands, as well as being involved in their incorporation into the existing platelet plug, creating a fibrin clot. The fibrin strands themselves are manufactured through the interaction of various coagulation factors, via a process known as the coagulation cascade.
After strand construction, these fibrin monomers are woven into the framework of the platelet plug, adding greater strength and stability.
Once woven into the platelet plug, and further stabilized with covalent cross-linking, a fibrin clot (the end goal of secondary hemostasis) is achieved. The fibrin clot is more durable than the platelet plug, and is more of a long term fix, allowing time for continued vascular repair.