But what mean those terms?... especially for the neutrino.
One distinguish left chiral objects from right chiral objects.
This difference, in general arbitrary, can be based on the rotation
of the polarity plane of a light
beam passing through a test material. Using a certain type of sugar
called dextrose, the polarity plane rotates to the right, when the
light beam is looked from the back.
Dextrose is then said to be of right chirality. That's the rule.
Most of the life molecules turn the polarity plane to the left:
they are said to be of left chirality.
But amino-acids, which are supposed to be at the origin of life,
are of right chirality.
This difference is a great mystery which could be linked to
the assymetry of weak interactions,
thus linked to the neutrinos.
Theoretically, a zero mass neutrino can only have a left helicity. It is very peculiar to the weak interaction, which produces only left helicity neutrinos. A neutrino could be of left or right chirality. But a zero mass neutrino having a left helicity would be always of left chirality... The terms "left" or "right" (often subscripted L and R) refer to the left or right chirality. In the limit of zero mass they correspond to the left or right helicity.