A churchwarden pipe is a tobacco pipe with a long stem. Some churchwarden pipes can be as long as 16 inches (40 cm). In German the style is referred to as "Lesepfeife" or "reading pipe," presumably because the longer stem allowed an unimpeded view of one's book, and smoke doesn't form near the reader's eyes, allowing one to look down.
Such pipes were very popular as an Oriental influence from the 17th century onwards in Europe. They remained most popular in Eastern Europe, as an emblem of the "Hussars," cavalry troops with roots in the Austro-Hungarian Empire, who went from Russia to France and England during the Napoleonic Wars and brought the pipes with them. It was even known as the "Hussar pipe" at the time. Engraved portraits exist of men smoking such an instrument. This long stem pipe type has its origins in the Ottoman Empire, geographically and historically.
Churchwarden pipes generally produce a cooler smoke due to the distance smoke must travel from the bowl to the mouthpiece. They have the added benefit of keeping the user's face further away from the heat and smoke produced by combustion in the bowl. They are also more prone to breakage since more pressure is placed on the tenon when the pipe is supported around the mouthpiece. Long ago, churchwarden pipes were made of clay and were common in taverns, and sometimes a set of pipes would have been owned by the establishment and used by different clients like other service items (plates, tankards, etc.).
Churchwarden pipes were reputedly named after churchwardens, or night watchmen of churches in the time that churches never locked their doors. These "churchwardens" couldn't be expected to go all night without a smoke, so they had pipes that were made with exceptionally long stems so the smoke and the pipe wouldn't be in their line of sight as they kept watch. Also made popular by the Lord of the Rings trilogy, Churchwardens have become highly desirable in recent years.