[Wikipedia] A Mars cycler (or Earth-Mars cycler) is a special kind of spacecraft trajectory that encounters Earth and Mars on a regular basis. The term Mars cycler may also refer to a spacecraft on a Mars cycler trajectory. The Aldrin cycler is an example of a Mars cycler.
In 1985, Buzz Aldrin theorized a so-called Aldrin Cycler corresponding to a single synodic period. The existence of such trajectories was calculated and confirmed later that year: a single eccentric loop around the sun from Earth to the Martian orbit in 146 days, spending the next 16 months beyond the orbit of Mars, and another 146 days from the Martian orbit back to Earth.