"Cleanliness is next to Godliness," a common phrase, describes humanity's high opinion of being clean.
 
Purposes of cleanliness include health, beauty, absence of offensive odor, avoidance of shame, and to avoid the spreading of dirt and contaminants to oneself and others. In the case of glass objects such as windows or windshields, the purpose can also be transparency.
 
Washing is one way of achieving cleanliness, usually with water and often some kind of soap or detergent.
 
Hygiene is commonly understood as preventing infection through cleanliness. In broader call, scientific terms hygiene is the maintenance of health and healthy living. Hygiene ranges from personal hygiene, through domestic up to occupational hygiene and public health; and involves healthy diet, cleanliness, and mental health.