What is a parsec?

A parsec is indeed a unit of distance that is equivalent to approximately 3.26 light years. It is used predominantly in astronomy to measure vast distances to stars and galaxies. The term "parsec" is derived from the method of measurement, where it represents the distance at which one astronomical unit subtends an angle of one arcsecond. This makes it a crucial unit for astronomers when dealing with the immense scales of the universe.

The other options do not correctly define a parsec. Measurements of time in astronomy do not relate to the term, and a classification system for stars or a type of star does not encompass the definition of a parsec. These options misrepresent the scientific context in which the term is primarily used, which focuses on distances rather than classifications or measurements of time.