A well-seasoned pipe is a cool-smoking pipe.

When one smokes tobacco out of a pipe, a layer of carbon builds up on the inside of the pipe. What this does is create an insulating layer of sorts, which keeps the bowl of the pipe cool. This layer of carbon, which is optimally around 1/8" thick, also keeps a wooden pipe from being burned as if it were a log in a fire.

If one were to go to their local tobacconist, some of them offer the service of seasoning one's pipe. They will actually use a machine to place a layer of carbon on the inside of the pipe, and use a tool to shape the layer so that it does not interfere with the smoking of the pipe - a ragged layer of carbon inside the pipe is almost as bad as none at all, because it will cause the pipe to be extremely hot in one's hands. Usually, this is undesirable, since most people smoke a pipe to relax, whether it contains tobacco or something else.

To season your own pipe, you should first fill the pipe one-quarter full with tobacco, smoke it slowly and avoid raising the bowl's temperature - If the bowl gets hot, you'll know you are doing this when you start getting moisture on your lips from the stem of the pipe when you are smoking it. If this happens, put out your pipe, and wait for it to cool and clean it out with a pipe cleaner before lighting it again. After 4 or 5 repetitions of this, you can increase the amount of tobacco you put in your pipe, and after 20 or so times, you should be able to fill the bowl completely. This process is long and tedious, but essential. A good rule of thumb is that you should smoke your pipe no more than twice a day during the seasoning process - you should not try to rush the process!

Information on seasoning your own pipe gleaned in part from https://id227.securedata.net/maisonducigare/howtochoose.htm and edited for clarity.