NEUTRAL DENSITY
  Neutral (particle) density is a parameter derived from the rate at which 
  particles are detected scaled by the probability of detecting individual
  particles. Neutral particle detectors commonly exclude ionized particles
  from entering the counting region of the instrument using a charged repeller
  grid. Density values are commonly reported in cgs units.

NEUTRAL COMPOSITION
  Neutral (particle) composition is a parameter which describes the total
  density of neutral particles in terms of constituent particle densities.

SUPERTHERMAL ION FLUX
  Superthermal ion flux is a measure of the rate at which ions (whose energies
  are high with respect to the characteristic temperature of the bulk
  distribution - 'superthermal') pass through a unit volume.

APPARENT FLOW ANGLE
  An apparent flow angle is the projection of a true flow angle into some
  reference plane.