If routing table contains several routes with the same dst-address, only one of them can be used to forward packets. This route is installed into FIB and marked as active.
When forwarding decision uses additional information, such as a source address of the packet, it is called policy routing. Policy routing is implemented as a list of policy routing rules, that select different routing table based on destination address, source address, source interface, and routing mark (can be changed by firewall mangle rules) of the packet.