What does passive smoking mean?

Passive smoking (also known as secondhand smoking, involuntary smoking, exposure to environmental tobacco smoke, or ETS exposure) occurs when smoke from one person's burning tobacco product (or the smoker's exhalation) is inhaled by others. Current scientific evidence shows that exposure to secondhand tobacco smoke causes death, disease and disability.

Passive smoking is one of the key issues leading to smoking bans in workplaces and indoor public places, including restaurants.

[edit] Long-term effects
Research has generated scientific evidence that secondhand smoke (i.e. in case of cigarette, a mixture of smoke released from the smoldering end of the cigarette and smoke exhaled by the smoker) causes the same problems as direct smoking, including heart disease,[5] cardiovascular disease, lung cancer, and lung ailments such as COPD, bronchitis and asthma.[6] Specifically, meta-analyses have shown lifelong non-smokers with partners who smoke in the home have a 20-30% greater risk of lung cancer, and those exposed to cigarette smoke in the workplace have an increased risk of 16-19%.[7]

A wide array of negative effects are attributed, in whole or in part, to frequent, long term exposure to second hand smoke. Some of the symptoms which have been or are frequently attributed to second hand smoke include:

Risk of lung cancer
The effect of passive smoking on lung cancer has been extensively studied. Studies from the USA (1986,[8][9] 1992,[10] 1997,[11] 2001,[12] 2003[13]), the UK (1998[14][15]), and Australia (1997[16]), as well as pooled international cohorts (2004[17]) have consistently shown a significant increase in relative risk among those exposed to passive smoke.
Risk of cancer[18]
Reviewing the evidence accumulated on a worldwide basis, the International Agency for Research on Cancer concluded in 2002 that "Involuntary smoking (exposure to secondhand or 'environmental' tobacco smoke) is carcinogenic to humans (Group 1)."[19]
Risk of heart disease[20]
Risk of miscarriage and birth defects[21]
Risk of sudden infant death syndrome (SIDS)[22]
Risk of developing asthma, both for children[23] and adults[24][25]
Risk of lung infections[26][27][28][29]
Risk of ear infections[30]
Risk of allergies and death of children[31]
Worsening of asthma, allergies, and other conditions[32]
Risk of learning difficulties,[33] although this may only be in children exposed before birth.[34] Animal models suggest a role for nicotine and carbon monoxide in neurocognitive problems
Although the nature of passive smoking makes study design problematic, meta-analyses from around the world suggest that dangers of passive smoking are significant.

It is estimated that passive smoking kills 53,000 nonsmokers per year, making it the 3rd leading cause of preventable death in the U.S.