It is a region of the H-R diagram, along which stars can be found to be arranged as they undergo helium core fusion.
It is the track followed by low-mass stars as they evolve off the main sequence, before their helium flash.
It is the track followed by high-mass stars as they undergo progressive fusion of different nuclei.
It is the track followed by low-mass stars as they age between their helium flash and the point at which their planetary nebula has been ejected.
It is the path in the H-R diagram followed by white dwarf stars as they age.