Image Source: Figure 3.2, Introduction to Modern Astrophysics, 2nd ed., Carroll & Ostlie, 2006.

Small periodic shift of the apparent positions of nearby stars due to the changing position of the Earth as it orbits the Sun. The nearer the star is, the larger the shift. The distance to stars in parsecs is simply 1/parallax, (or in light years it is 3.2616 divided by the parallax) where the parallax is in arcseconds.

Some or all content above used with permission from J. H. Wittke.