How does the orbit of Halley’s Comet differ from a parabolic comet orbit?

The orbit of Halley’s Comet differs from a parabolic orbit primarily in its periodicity and gravitational binding to the solar system.

In celestial mechanics, an orbit is defined by its eccentricity ($e$):
* Parabolic orbits have an eccentricity of exactly $e=1$, representing an open path where an object passes the Sun once and does not return.1
* Halley’s Comet follows a bound, elliptical orbit with an eccentricity of $e<1$, which causes it to return to the inner solar system at regular intervals.21

English astronomer Edmond Halley famously identified this periodic nature by observing that comets seen in 1531, 1607, and 1682 shared similar orbital characteristics, leading him to correctly predict their return. While many comets may appear to have nearly parabolic orbits during their first pass into the inner solar system, Halley’s Comet is a confirmed periodic object. Its orbital period averages approximately 76 years, though this duration fluctuates between 74.5 and 79 years due to the gravitational influence of the planets.21