π1 or Π1 or Pi1 may refer to:
Mathematics π1, a notation for the scalar projection onto the first component π1, the fundamental group of a topological space Π1, the fundamental groupoid of a topological space Π01, or Π1, a classification in the arithmetical hierarchy
Other uses Yudo π1 (Pi1), a car model Pi1 (gene), a gene found in Oryza sativa for fungus resistance Pi1, a type of torpedo warhead used by Germany in World War II; see List of World War II torpedoes of Germany
See also
Pil (disambiguation) PII (disambiguation) P1 (disambiguation) (; romanized "p1"; pronounced "pi1") Pi (disambiguation) π (disambiguation)