From what geometric method is the parsec unit derived?

Parallax

The parsec ($ ext{pc}$) is a unit favored by professional astronomers because its definition is directly linked to a primary geometric technique for determining stellar distances: parallax. Parallax involves observing the slight, apparent shift in a star's position over time as the Earth moves along its orbit around the Sun. A parsec is formally defined as the distance to a celestial object at which one Astronomical Unit (the distance from Earth to the Sun) subtends an angle of exactly one arcsecond. Because this derivation is mathematically clean and directly linked to observational data gathered through parallax measurements, it simplifies complex professional calculations for mapping the galaxy, even though the light-year might be used more often in public communication.