A comment on this question says to "check the cluster". What does it mean to "check the cluster"? I'm guessing it's a website. I did an internet search and http://www.hamcluster.net/Map.aspx seems to be limited to DX.
A DX cluster is a venue (a website or Telnet session) where amateurs may post information about the callsign and frequency of a desirable DX station, so that others may see the posts and then work them if desired.
A DX cluster is a network [or "cluster"] of computers, each running a software package dedicated to gathering, and disseminating, information on amateur radio DX (long-distance contact) activities.
The first DX cluster software, PacketCluster2 was realized by US radio amateur Dick Newell, AK1A in the late 1980s, and quickly became popular as a means of exchanging DX-related information. Before the Internet became widely available, the nodes running the cluster software would connect via radio links at certain frequencies allocated within the amateur radio bands. Users of the system would then connect to a node using frequencies different to those used by the nodes.
When the Internet became widely available, the system was expanded to make use of telnet connections to Internet nodes, in addition to the already established packet radio nodes. Users of internet nodes connect to a particular node using telnet client software.
"DX" (long distance) can have different meanings, depending on what band you are using and where you are located. http://on4kst.com/chat/start.php is the one I use during 160m CW contests. It lists all the bands EXCEPT for the "DX bands" 10, 12, 15, and 20.
They started using radio, well before the Internet. Most of those were local DX "clusters" (though they were not called that back then) on VHF and UHF repeaters. Then Packet Radio came along, followed by PacketCluster software which came into wide use.
Types of DX clusters
There are different types of clusters. Some clusters are not necessarily about a foreign country (DX). Assuming you are in the USA, a post may be about a station in a rare US state or grid square, for example. "The" cluster implies that there is only one. Thus when you were told that, you may have been given incomplete information.
Telnet clusters are accessed from a terminal window (or command prompt), and are text-based rather than graphical.
A DX Cluster can also be used to announce upcoming contests and DXpeditions, as well as enable users to chat amongst themselves.