c1 refers to the first condition, c2 to the second, etc.
So in e.g.
c1 refers to IsEqual(_Char,null)
c2 refers to CharacterIsIgnoringGroundSurface(_Char)
and the string at the top clarifies that the first three must return false and the last one has to return true, i.e. the character must be not null, not ignoring ground surfaces, and not a dead, and the character must be a player.