Any mass of ice that occurs on the Earth's continents or surface waters. Such masses form wherever substantial amounts of liquid water freeze and remain in the solid state for some period of time. Examples include glaciers, icebergs, sea ice, and ground ice associated with permafrost.

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Largest geographic biotic unit, a major community of plants and animals with similar requirements of environmental conditions. It includes various communities and developmental stages of communities and is named for the dominant type of vegetation, such as grassland or coniferous forest. Several similar biomes constitute a biome type; for example, the temperate deciduous forest biome type includes the deciduous forest biomes of Asia, Europe, and North America. The standard European term for biome is “major life zone.”

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Process of developing abstract rules or mental constructs based on sensory experience. Concept formation figures prominently in cognitive development and was a subject of great importance to Jean Piaget, who argued that learning entails an understanding of a phenomenon's characteristics and how they are logically linked. Noam Chomsky later argued that certain cognitive structures (such as basic grammatical rules) are innate in human beings. Both scholars held that, as a concept emerges, it becomes subject to testing: a child's concept of “bird,” for example, will be tested against specific instances of birds. The human capacity for play contributes importantly to this process by allowing for consideration of a wide range of possibilities.

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