π (EN)

letter, symbol

letter “π”

1. the 16th letter of the Greek alphabet
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   The teacher wrote a π on the blackboard.

symbol “π”

1. (mathematics) the mathematical constant pi, approximately 3.1416, equal to the ratio of a circle's circumference to its diameter
   In our geometry lesson, we calculated the circumference of circles using π.
2. (physics) a type of meson particle called a pion
   Physicists observed the decay of the π meson during the experiment.
3. (mathematics) a symbol used to denote a homotopy group in algebraic topology
   The topologist explained how π₁ measures the fundamental group of a space.
4. (mathematics) the prime-counting function, which gives the number of primes less than or equal to a given number
   Mathematicians study the behavior of π(n), the prime-counting function.
5. (phonetics) a symbol representing a voiced labial click consonant in certain phonetic alphabets
   In phonetic transcription, π is sometimes used to represent a labial click sound.