Why was the parsec invented?
AU is defined as Earth-Sun average distance. On the contrast, Parsec is more general, relating parallax with AU. 1 parsec is the radius of a circle with 1 AU arc subtending 1" at the center.
1 parsec = 206264.8 AU. Parsec can be converted to light year units using 1 parsec = ,3.28 light years, nearly.