Doppler effect: alteration in the observed frequency of a sound due to motion of either the source or the observer.
Doppler shift: the actual change in frequency due to the relative motion of source and observer.
Definition found in OpenStax University Physics. Authored by: OpenStax CNX. Located at: https://cnx.org/contents/1Q9uMg_a@10.16:Gofkr9Oy@15. License: CC BY: Attribution.