Generally speaking, a route server is a network device that does not participate directly in routing, but carries an entire routing table that other devices may refer to. Often times, this is a router that carries the entire Internet BGP routing table (currently over 220,000 routes).
More commonly, a route server is a router that a BGP operator will use to examine her announced
<acronym title="Autonomous System Number">ASN
</acronym> and prefixes as viewed by the Internet. This external view is imperative when troubleshooting BGP issues or just checking up on your announcements. The most commonly used commands (by me) are
show ip bgp <prefix> and
show ip bgp regexp _<ASN>$.
I most commonly use the primary route server at the Oregon Internet Exchange: route-views.oregon-ix.net. The AT&T IP Services route server at route-server.ip.att.net is also a good choice. You can find a comprehensive list of route servers at traceroute.org.