A Hayashi track is a track along a H-R diagram (HRD) showing the evolution of a pre-main-sequence star, i.e., each point on the track indicates the position of that body at some point in its life. In particular, it outlines a phase in which the star is fully convective, something that happens in the early lifetimes of stars of up to 3 solar masses. The exact track depends upon the mass, metallicity and helium abundance (mass fractions) of the star. The tracks were worked out numerically and was and are checked against observations of star-forming regions. Stars which do not remain fully convective (i.e., larger than red dwarves) then follow the Henyey track.