A route server is a type of Server that is used in Network engineering.
The original role of a route server was to be an easily accessible source of Routing information about a particular network, for other machines as well as for remote network engineers that would need that information to troubleshoot network issues.
[1] Modern implementations have taken on more roles, the most common being Route aggregation.
The Border Gateway Protocol normally requires Peers to maintain sessions with every other peer they could potentially send or receive traffic from, but a route server can aggregate these sessions and make them available for several peers.
[2][3]