Quick answer
Stacy is a boy/girl name.
Meaning and history
As a feminine name it is commonly considered a diminutive of Anastasia, though it was originally used independently of that name, which was rare in America in the 1950s when Stacy began becoming popular. It had earlier been in use as an uncommon masculine name, borrowed from the surname Stacy or Stacey (derived from Stace, a medieval form of Eustace ).
Notes and context
Usage: english