Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings:

• a piece of information
• the act or result of understanding the inner nature of things or of seeing intuitively (called noesis in Greek)
• an introspection
• the power of acute observation and deduction, discernment, and perception, called intellection or noesis
• An understanding of cause and effect based on the identification of relationships and behaviors within a model, context, or scenario (see artificial intelligence)

An insight that manifests itself suddenly, such as understanding how to solve a difficult problem, is sometimes called by the German word Aha-Erlebnis. The term was coined by the German psychologist and theoretical linguist Karl Bühler. It is also known as an epiphany, eureka moment or (for cross word solvers) the penny dropping moment (PDM). Sudden sickening realisations often identify a problem rather than solving it, so Uh-oh rather than Aha moments are further seen in negative insight. A further example of negative insight is chagrin which is annoyance at the obviousness of a solution missed up until the point of insight, an example of this being the Homer Simpson's catchphrase exclamation, D'oh!.