[′laŋ‚myu̇r ′plaz·mə ‚frē·kwən·sē] (plasma physics) The frequency of nonpropagating oscillations in a plasma; in rationalized mks units, it is (ne2/ε0m)1/2, where e and m are the charge and mass of the oscillating electrons or ions, n is their number density, and ε0 is the permittivity of empty space. Also known as plasma frequency.