Smoking is a recreational drug activity, which involves lighting anything made of tobacco and tar, and then inhaling the fumes. By the mid-20th Century, however, smoking was looked down upon, largely because of the then-newly discovered health hazards of the activity either to the smoker directly, or to those close by, particularly in the respiratory system. In some cases, smoking was even banned in certain areas, such as flights.
Behind the scenes
Smoking is a recurring element in the Metal Gear series, with it being done by the player characters and, in some cases, at least one supporting character. In the games, various supporting characters will usually tell off the main character whenever they smoke. The only known exceptions of this are in Metal Gear Solid: Peace Walker and Metal Gear Solid V, the former because most of the characters are smokers themselves.