A chipper is an occassional tobacco smoker who isn't subject to the heavy level that is typical of addicted smokers. Such occassional users of tobacco are also dubbed social smokers which is similar in meaning to social drinker. Chippers are given as an example in The Tipping Point; if chippers begin smoking above a certain threshold (or tipping point), then they will develop regular cravings and become addicted.
This term is also used to refer to the occassional (or weekend) heroin user.
A chipper is also a device that mechanically breaks down a substance into small pieces (or chips). For instance, logs or branches can be fed into wood chippers to generate smaller chips. Chippers are also used to break up plastic bottles before recycling.