In meteorology, a cloud is a visible mass of liquid droplets or frozen crystals made of water or various chemicals suspended in the atmosphere above the surface of a planetary body. These suspended particles are also known as aerosols. Clouds in earth's atmosphere are studied in the cloud physics branch of meteorology. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. In general, precipitation will fall to the surface; an exception is virga, which evaporates before reaching the surface.

Clouds can show convective development like cumulus, appear in layered sheets such as stratus, or take the form of thin fibrous wisps, as in the case of cirrus. Prefixes are used in connection with clouds: strato- for low cumuliform-category clouds that show some stratiform characteristics, nimbo- for thick stratiform clouds that can produce moderate to heavy precipitation, alto- for middle clouds, and cirro- for high clouds. Whether or not a cloud is low, middle, or high level depends on how far above the ground its base forms.

Dust consists of particles in the atmosphere that come from various sources such as soil dust lifted by wind (an Aeolian process), volcanic eruptions, and pollution. Dust in homes, offices, and other human environments contains small amounts of plant pollen, human and animal hairs, textile fibers, paper fibers, minerals from outdoor soil, human skin cells, burnt meteorite particles and many other materials which may be found in the local environment.

Dust may worsen hay fever. Circulating outdoor air through a house by keeping doors and windows open, or at least slightly ajar, may reduce the risk of hay fever-causing dust. In colder climates, occupants seal even the smallest air gaps, and eliminate outside fresh air circulating inside the house. So it is essential to manage dust and airflow.

House dust mites are ubiquitous everywhere humans live indoors. Positive tests for dust mite allergies are extremely common among people with asthma. Dust mites are microscopic arachnids whose primary food is dead human skin cells. They do not actually live on people, though. It is probably not possible to entirely eradicate them. They and their feces and other allergens they produce are major constituents of house dust, but because they are so heavy they are not long suspended in the air. They generally are on the floor and other surfaces, until disturbed (by walking, for example). Sources suggest it could take somewhere between 20 minutes and 2 hours for them to settle back down out of the air. Dust mites are a nesting species that prefer a dark, warm and humid climate, and they therefore flourish in mattresses, bedding, upholstered furniture, and carpets. Their feces include enzymes that are released upon contact with a moist surface, as happens when a person breathes it in, and these enzymes actually kill cells within the human body. Sources suggest that house dust mites did not become a problem until humans began to use textiles, such as western style blankets and clothing.

Data ( /ˈdeɪtə/ DAY-tə, /ˈdætə/ DA-tə, or /ˈdɑːtə/ DAH-tə) are values of qualitative or quantitative variables, belonging to a set of items. Data in computing (or data processing) are often represented by a combination of items organized in rows and multiple variables organized in columns. Data are typically the results of measurements and can be visualised using graphs or images. Data as an abstract concept can be viewed as the lowest level of abstraction from which information and then knowledge are derived. Raw data, i.e., unprocessed data, refers to a collection of numbers, characters and is a relative term; data processing commonly occurs by stages, and the "processed data" from one stage may be considered the "raw data" of the next. Field data refers to raw data collected in an uncontrolled in situ environment. Experimental data refers to data generated within the context of a scientific investigation by observation and recording.

The word data is the plural of datum, neuter past participle of the Latin dare, "to give", hence "something given". In discussions of problems in geometry, mathematics, engineering, and so on, the terms givens and data are used interchangeably. Such usage is the origin of data as a concept in computer science or data processing: data are numbers, words, images, etc., accepted as they stand.