Most operating systems store the DNS data. This saves time when you visit the same websites over and over because the domain name does not need to be converted to an IP so the computer can understand it.
You see computers do not understand a normal domain name for a website like http://tips4pc.com so it turns this to an IP (internet protocol) address so it can read it. Therefore to save having to convert an address each time it is requested, the DNS data is stored in the DNS cache.
Sometimes it is good to clear out the DNS cache so check out this video for more info.